diff --git a/.github/workflows/node.yml b/.github/workflows/node.yml
index c1e03e8d7..37b7cac3c 100644
--- a/.github/workflows/node.yml
+++ b/.github/workflows/node.yml
@@ -81,4 +81,14 @@ jobs:
         if: steps.test_units.outcome == 'failure'
         run: |
           echo "::notice::Run \`npm run test:unit\` in your dev environment for a detailed report about failed unit tests"
+          exit 1
+      - name: Ensure all units are covered
+        if: steps.changed-files.outputs.any_changed == 'true'
+        id: test_unit_missing
+        run: npm run test:unit:missing
+        continue-on-error: true
+      - name: If there are missing unit tests, highlight debug tools
+        if: steps.test_unit_missing.outcome == 'failure'
+        run: |
+          echo "::notice::Run \`npm run test:unit -- run && npm run test:unit:missing\` in your dev environment to see which units are missing a test companion"
           exit 1
\ No newline at end of file
diff --git a/@internal/Directory/createAt.ts b/@internal/Directory/createAt.ts
new file mode 100644
index 000000000..ee809167e
--- /dev/null
+++ b/@internal/Directory/createAt.ts
@@ -0,0 +1,21 @@
+import {
+  mkdirSync,
+} from 'node:fs';
+
+import type FilesystemPath from '../FilesystemPath';
+
+import {
+  serialized,
+} from '../FilesystemPath';
+
+const Directory_createAt = (
+  givenPath: FilesystemPath,
+): void => {
+  mkdirSync(serialized(givenPath), {
+    recursive: true,
+  });
+};
+
+export {
+  Directory_createAt,
+};
diff --git a/@internal/Directory/definition.assembled.members.ts b/@internal/Directory/definition.assembled.members.ts
new file mode 100644
index 000000000..74102dc5d
--- /dev/null
+++ b/@internal/Directory/definition.assembled.members.ts
@@ -0,0 +1,3 @@
+export {
+  Directory_createAt as createAt,
+} from './createAt';
diff --git a/@internal/Directory/definition.assembled.ts b/@internal/Directory/definition.assembled.ts
new file mode 100644
index 000000000..700322793
--- /dev/null
+++ b/@internal/Directory/definition.assembled.ts
@@ -0,0 +1 @@
+export * as Directory from './definition.assembled.members.ts';
diff --git a/@internal/Directory/exports.object.primary.ts b/@internal/Directory/exports.object.primary.ts
new file mode 100644
index 000000000..8ac7983ac
--- /dev/null
+++ b/@internal/Directory/exports.object.primary.ts
@@ -0,0 +1 @@
+export * from './definition.assembled.ts';
diff --git a/@internal/Directory/index.ts b/@internal/Directory/index.ts
new file mode 100644
index 000000000..3f4016845
--- /dev/null
+++ b/@internal/Directory/index.ts
@@ -0,0 +1,3 @@
+export {
+  Directory as default,
+} from './exports.object.primary.ts';
diff --git a/@internal/File/contentsReadFrom.ts b/@internal/File/contentsReadFrom.ts
new file mode 100644
index 000000000..912860c0d
--- /dev/null
+++ b/@internal/File/contentsReadFrom.ts
@@ -0,0 +1,25 @@
+import {
+  readFileSync,
+} from 'node:fs';
+
+import type FilesystemPath from '../FilesystemPath';
+
+import {
+  serialized,
+} from '../FilesystemPath';
+
+const File_contentsReadAt = (
+  givenPath: FilesystemPath,
+): string => {
+  const someAbsolutePath = serialized(givenPath);
+
+  const contentsFromGivenPath = readFileSync(someAbsolutePath, {
+    encoding: 'utf8',
+  });
+
+  return contentsFromGivenPath;
+};
+
+export {
+  File_contentsReadAt as File_contentsReadFrom,
+};
diff --git a/@internal/File/definition.assembled.members.ts b/@internal/File/definition.assembled.members.ts
new file mode 100644
index 000000000..66f77c4ed
--- /dev/null
+++ b/@internal/File/definition.assembled.members.ts
@@ -0,0 +1,11 @@
+export {
+  File_doesExistAt as doesExistAt,
+} from './doesExistAt';
+
+export {
+  File_contentsReadFrom as contentsReadFrom,
+} from './contentsReadFrom';
+
+export {
+  File_write as write,
+} from './write';
diff --git a/@internal/File/definition.assembled.ts b/@internal/File/definition.assembled.ts
new file mode 100644
index 000000000..838989058
--- /dev/null
+++ b/@internal/File/definition.assembled.ts
@@ -0,0 +1 @@
+export * as File from './definition.assembled.members.ts';
diff --git a/@internal/File/doesExistAt.ts b/@internal/File/doesExistAt.ts
new file mode 100644
index 000000000..67d411619
--- /dev/null
+++ b/@internal/File/doesExistAt.ts
@@ -0,0 +1,20 @@
+import {
+  existsSync,
+} from 'node:fs';
+
+import type FilesystemPath from '../FilesystemPath';
+
+import {
+  serialized,
+} from '../FilesystemPath';
+
+const File_doesExistAt = (
+  givenPath: FilesystemPath,
+): boolean => {
+  const derivedAbsolutePath = serialized(givenPath);
+  return existsSync(derivedAbsolutePath);
+};
+
+export {
+  File_doesExistAt,
+};
diff --git a/@internal/File/exports.object.primary.ts b/@internal/File/exports.object.primary.ts
new file mode 100644
index 000000000..8ac7983ac
--- /dev/null
+++ b/@internal/File/exports.object.primary.ts
@@ -0,0 +1 @@
+export * from './definition.assembled.ts';
diff --git a/@internal/File/exports.toolbox.ts b/@internal/File/exports.toolbox.ts
new file mode 100644
index 000000000..a5157b743
--- /dev/null
+++ b/@internal/File/exports.toolbox.ts
@@ -0,0 +1,3 @@
+export * from './toPath';
+
+export * from './contentsReadFrom';
diff --git a/@internal/File/index.ts b/@internal/File/index.ts
new file mode 100644
index 000000000..89a23c0b7
--- /dev/null
+++ b/@internal/File/index.ts
@@ -0,0 +1,5 @@
+export {
+  File as default,
+} from './exports.object.primary.ts';
+
+export * from './exports.toolbox.ts';
diff --git a/@internal/File/toPath.ts b/@internal/File/toPath.ts
new file mode 100644
index 000000000..495c7aaf8
--- /dev/null
+++ b/@internal/File/toPath.ts
@@ -0,0 +1,16 @@
+import {
+  fileURLToPath,
+} from 'node:url';
+
+import FilesystemPath from '../FilesystemPath';
+
+const toPath = (
+  givenFile: URL,
+): FilesystemPath => {
+  const absolutePathToFile = fileURLToPath(givenFile);
+  return FilesystemPath.parsedFrom(absolutePathToFile);
+};
+
+export {
+  toPath,
+};
diff --git a/@internal/File/write.ts b/@internal/File/write.ts
new file mode 100644
index 000000000..d79328579
--- /dev/null
+++ b/@internal/File/write.ts
@@ -0,0 +1,27 @@
+import {
+  writeFileSync,
+} from 'node:fs';
+
+import type FilesystemPath from '../FilesystemPath';
+
+import {
+  serialized,
+} from '../FilesystemPath';
+
+const File_write = (
+  {
+    contents: givenContents,
+    to: givenPath,
+  }: {
+    contents: string;
+    to: FilesystemPath;
+  },
+): void => {
+  writeFileSync(serialized(givenPath), givenContents, {
+    encoding: 'utf8',
+  });
+};
+
+export {
+  File_write,
+};
diff --git a/@internal/FilesystemPath/definition.declared.augmentation.ts b/@internal/FilesystemPath/definition.declared.augmentation.ts
new file mode 100644
index 000000000..fcf8255fc
--- /dev/null
+++ b/@internal/FilesystemPath/definition.declared.augmentation.ts
@@ -0,0 +1,29 @@
+import {
+  FilesystemPath,
+} from './definition.declared.ts';
+
+import {
+  FilesystemPath_from,
+} from './from.ts';
+
+import {
+  FilesystemPath_parsedFrom,
+} from './parsedFrom.ts';
+
+import {
+  FilesystemPath_resolved,
+} from './resolved.ts';
+
+FilesystemPath.from /*      */ = FilesystemPath_from;
+FilesystemPath.parsedFrom /**/ = FilesystemPath_parsedFrom;
+FilesystemPath.resolved /*  */ = FilesystemPath_resolved;
+
+declare module './definition.declared.ts' {
+  namespace FilesystemPath {
+    export {
+      FilesystemPath_from /*      */ as from,
+      FilesystemPath_parsedFrom /**/ as parsedFrom,
+      FilesystemPath_resolved /*  */ as resolved,
+    };
+  }
+}
diff --git a/@internal/FilesystemPath/definition.declared.ts b/@internal/FilesystemPath/definition.declared.ts
new file mode 100644
index 000000000..c2e06e61e
--- /dev/null
+++ b/@internal/FilesystemPath/definition.declared.ts
@@ -0,0 +1,21 @@
+import type {
+  ParsedPath,
+} from 'node:path';
+
+import {
+  Effect,
+} from 'effect';
+
+type FilesystemPath = ParsedPath;
+
+function FilesystemPath(
+  namespaceOnly: never = Effect.die(
+    () => new Error(`Unexpected call of module augmentation provision for ${FilesystemPath.name}.`),
+  ).pipe(Effect.runSync),
+): never {
+  return namespaceOnly;
+}
+
+export {
+  FilesystemPath,
+};
diff --git a/@internal/FilesystemPath/definition.declared.withAugmentation.ts b/@internal/FilesystemPath/definition.declared.withAugmentation.ts
new file mode 100644
index 000000000..f11cfa9fa
--- /dev/null
+++ b/@internal/FilesystemPath/definition.declared.withAugmentation.ts
@@ -0,0 +1,3 @@
+import './definition.declared.augmentation.ts';
+
+export * from './definition.declared.ts';
diff --git a/@internal/FilesystemPath/exports.object.primary.ts b/@internal/FilesystemPath/exports.object.primary.ts
new file mode 100644
index 000000000..52e0e7aef
--- /dev/null
+++ b/@internal/FilesystemPath/exports.object.primary.ts
@@ -0,0 +1 @@
+export * from './definition.declared.withAugmentation.ts';
diff --git a/@internal/FilesystemPath/exports.toolbox.ts b/@internal/FilesystemPath/exports.toolbox.ts
new file mode 100644
index 000000000..3f5ba70fe
--- /dev/null
+++ b/@internal/FilesystemPath/exports.toolbox.ts
@@ -0,0 +1 @@
+export * from './serialized';
diff --git a/@internal/FilesystemPath/from.ts b/@internal/FilesystemPath/from.ts
new file mode 100644
index 000000000..071560e76
--- /dev/null
+++ b/@internal/FilesystemPath/from.ts
@@ -0,0 +1,39 @@
+import type {
+  FilesystemPath,
+} from './definition.declared.ts';
+
+const FilesystemPath_from = (
+  givenPath: FilesystemPath,
+  {
+    name: nameMutatedFrom = ($0) => $0,
+    extension: extensionMutatedFrom = ($0) => $0,
+  }: {
+    name?: (
+      originalName: string,
+    ) => string;
+    extension?: (
+      originalExtension: string,
+    ) => string;
+  },
+): FilesystemPath => {
+  const mutablePath = {
+    ...givenPath,
+  };
+
+  mutablePath.name = nameMutatedFrom(mutablePath.name);
+  const mutatedExtension = extensionMutatedFrom(mutablePath.ext);
+
+  if (
+    (0 < mutatedExtension.length)
+    && !mutatedExtension.startsWith('.')
+  ) throw new Error(`Extension must start with a period when not empty: ${mutatedExtension}`); // eslint-disable-line no-restricted-syntax -- TODO replace with `Attempt`
+
+  mutablePath.ext = mutatedExtension;
+  mutablePath.base = `${mutablePath.name}${mutablePath.ext}`;
+
+  return mutablePath;
+};
+
+export {
+  FilesystemPath_from,
+};
diff --git a/@internal/FilesystemPath/index.ts b/@internal/FilesystemPath/index.ts
new file mode 100644
index 000000000..63c02974e
--- /dev/null
+++ b/@internal/FilesystemPath/index.ts
@@ -0,0 +1,5 @@
+export {
+  FilesystemPath as default,
+} from './exports.object.primary.ts';
+
+export * from './exports.toolbox.ts';
diff --git a/@internal/FilesystemPath/parsedFrom.ts b/@internal/FilesystemPath/parsedFrom.ts
new file mode 100644
index 000000000..dfbde808c
--- /dev/null
+++ b/@internal/FilesystemPath/parsedFrom.ts
@@ -0,0 +1,3 @@
+export {
+  parse as FilesystemPath_parsedFrom,
+} from 'node:path';
diff --git a/@internal/FilesystemPath/resolved.ts b/@internal/FilesystemPath/resolved.ts
new file mode 100644
index 000000000..74a0f06ed
--- /dev/null
+++ b/@internal/FilesystemPath/resolved.ts
@@ -0,0 +1,33 @@
+import {
+  resolve,
+} from 'node:path';
+
+import type {
+  FilesystemPath,
+} from './definition.declared.ts';
+
+import {
+  FilesystemPath_parsedFrom,
+} from './parsedFrom';
+
+import {
+  serialized,
+} from './serialized';
+
+const FilesystemPath_resolved = (
+  {
+    from: givenRoot,
+    to: givenPathFromTargetToRoot,
+  }: {
+    from: FilesystemPath;
+    to: string;
+  },
+): FilesystemPath => {
+  const absolutePathToRoot = serialized(givenRoot);
+  const absolutePathToTarget = resolve(absolutePathToRoot, givenPathFromTargetToRoot);
+  return FilesystemPath_parsedFrom(absolutePathToTarget);
+};
+
+export {
+  FilesystemPath_resolved,
+};
diff --git a/@internal/FilesystemPath/serialized.ts b/@internal/FilesystemPath/serialized.ts
new file mode 100644
index 000000000..acb03ec7a
--- /dev/null
+++ b/@internal/FilesystemPath/serialized.ts
@@ -0,0 +1,3 @@
+export {
+  format as serialized,
+} from 'node:path';
diff --git a/package.json b/package.json
index bbd6cad73..5f25e1b6a 100644
--- a/package.json
+++ b/package.json
@@ -8,6 +8,7 @@
     "build": "run-p type-check \"build-only {@}\" --",
     "preview": "vite preview",
     "test:unit": "vitest",
+    "test:unit:missing": "jiti vitest/ensure-all-units-have-test-companion.ts",
     "prepare": "cypress install && husky",
     "test:e2e": "start-server-and-test preview http://localhost:4173 'cypress run --e2e'",
     "test:e2e:dev": "start-server-and-test 'vite dev --port 4173' http://localhost:4173 'cypress open --e2e'",
diff --git a/scripts/stubbed-test-suites/main.ts b/scripts/stubbed-test-suites/main.ts
new file mode 100644
index 000000000..0f386674e
--- /dev/null
+++ b/scripts/stubbed-test-suites/main.ts
@@ -0,0 +1,79 @@
+import Directory from '../../@internal/Directory';
+import File from '../../@internal/File';
+import FilesystemPath from '../../@internal/FilesystemPath';
+
+interface TestCompanionCreationResult {
+  created: boolean;
+  pathForTestFile: string;
+}
+
+// take a given file path and generate a stub for a test suite
+function createAndSaveTestCompanionForUnitWith(
+  givenAbsolutePath: string,
+): TestCompanionCreationResult {
+  const componentsOfAbsolutePath = givenAbsolutePath.split('/');
+  const fileNameWithExtension = componentsOfAbsolutePath.pop() ?? '';
+  const [fileName, fileExtension] = fileNameWithExtension.split('.');
+
+  if (
+    !fileName || !fileExtension
+  ) throw new Error(`Could not parse file name and extension from: ${givenAbsolutePath}`); // eslint-disable-line no-restricted-syntax -- "@/library/Attempt is not accessible outside of src"
+
+  const testFileName = `${fileName}.test.${fileExtension}`;
+  const absolutePathToTestCompanion = [...componentsOfAbsolutePath, testFileName].join('/');
+  const symbolName = 'someSymbol';
+
+  const contentsOfTestCompanion = `import {
+  describe,
+} from 'vitest';
+
+import {
+  ${symbolName},
+} from './${fileNameWithExtension}';
+
+describe.todo(${symbolName});
+`;
+
+  const pathToTestCompanion = FilesystemPath.parsedFrom(absolutePathToTestCompanion);
+  const pathToDirectoryOfTestCompanion = FilesystemPath.parsedFrom(pathToTestCompanion.dir);
+
+  if (
+    !File.doesExistAt(pathToDirectoryOfTestCompanion)
+  ) Directory.createAt(pathToDirectoryOfTestCompanion);
+
+  const testCompanionShouldBeCreated = !File.doesExistAt(pathToTestCompanion);
+
+  if (
+    testCompanionShouldBeCreated
+  ) File.write({
+    contents: contentsOfTestCompanion,
+    to      : pathToTestCompanion,
+  });
+
+  return {
+    created        : testCompanionShouldBeCreated,
+    pathForTestFile: absolutePathToTestCompanion,
+  };
+}
+
+const inputPath = process.argv[2];
+
+if (!inputPath) {
+  console.error('Usage: npx jiti scripts/generate-stub-for-test-suite.ts <path-to-source-file.ts>');
+  process.exit(1);
+}
+
+// eslint-disable-next-line no-restricted-syntax -- "@/library/Attempt is not accessible outside of src"
+try {
+  const result = createAndSaveTestCompanionForUnitWith(inputPath);
+
+  const messageForResult = result.created
+    ? `Created test stub: ${result.pathForTestFile}`
+    : `Test file already exists: ${result.pathForTestFile}`;
+
+  console.log(messageForResult);
+}
+catch (err) {
+  console.error('Error:', (err as Error).message);
+  process.exit(1);
+}
diff --git a/src/features/TextToImage/Client/SDXL/toSharkUIOutput/Image/Description/all.test.ts b/src/features/TextToImage/Client/SDXL/toSharkUIOutput/Image/Description/all.test.ts
new file mode 100644
index 000000000..6a87739f4
--- /dev/null
+++ b/src/features/TextToImage/Client/SDXL/toSharkUIOutput/Image/Description/all.test.ts
@@ -0,0 +1,9 @@
+import {
+  describe,
+} from 'vitest';
+
+import {
+  toSharkUIOutput_Image_Description_all,
+} from './all.ts';
+
+describe.todo(toSharkUIOutput_Image_Description_all);
diff --git a/tsconfig.node.json b/tsconfig.node.json
index 50dd89ca6..8ff9caf19 100644
--- a/tsconfig.node.json
+++ b/tsconfig.node.json
@@ -3,8 +3,11 @@
   "include": [
     "*.config.*",
     "eslint.*",
+    "@internal/**/*",
+    "vitest/**/*",
     "cypress/eslint.config.*",
     "cypress/package.d.ts",
+    "scripts/**/*"
   ],
   "compilerOptions": {
     "noEmit": true,
@@ -15,6 +18,7 @@
     "types": [
       "node",
       "vite/client",
-    ]
+    ],
+    "allowImportingTsExtensions": true
   }
 }
diff --git a/vite.config.ts b/vite.config.ts
index 1d0452381..6753ff841 100644
--- a/vite.config.ts
+++ b/vite.config.ts
@@ -1,8 +1,3 @@
-import {
-  fileURLToPath,
-  URL,
-} from 'node:url';
-
 import vue from '@vitejs/plugin-vue';
 
 import {
@@ -12,6 +7,14 @@ import {
 import vueDevTools from 'vite-plugin-vue-devtools';
 import vuetify from 'vite-plugin-vuetify';
 
+import {
+  toPath,
+} from './@internal/File';
+
+import {
+  serialized,
+} from './@internal/FilesystemPath';
+
 // https://vite.dev/config/
 const viteConfig = defineConfig({
   plugins: [
@@ -27,7 +30,7 @@ const viteConfig = defineConfig({
   ],
   resolve: {
     alias: {
-      '@': fileURLToPath(new URL('./src', import.meta.url)),
+      '@': serialized(toPath(new URL('./src', import.meta.url))),
     },
   },
 });
diff --git a/vitest.config.ts b/vitest.config.ts
index 12fc411ca..dd0a74ed6 100644
--- a/vitest.config.ts
+++ b/vitest.config.ts
@@ -1,13 +1,18 @@
-import {
-  fileURLToPath,
-} from 'node:url';
-
 import {
   mergeConfig,
   defineConfig,
   configDefaults,
+  coverageConfigDefaults,
 } from 'vitest/config';
 
+import {
+  toPath,
+} from './@internal/File';
+
+import {
+  serialized,
+} from './@internal/FilesystemPath';
+
 import viteConfig from './vite.config';
 
 const vitestConfig = mergeConfig(
@@ -16,7 +21,26 @@ const vitestConfig = mergeConfig(
     test: {
       environment: 'jsdom',
       exclude    : [...configDefaults.exclude, 'e2e/**'],
-      root       : fileURLToPath(new URL('./', import.meta.url)),
+      root       : serialized(toPath(new URL('./', import.meta.url))),
+      coverage   : {
+        enabled: true,
+        include: [
+          'src/library/**/*.ts',
+          'src/features/**/*.ts',
+        ],
+        exclude: [
+          ...coverageConfigDefaults.exclude,
+          'src/**/index.ts', // barrel files as entry points
+          'src/**/exports.*.ts', // barrel files as export control
+          'src/**/definition.assembled*.ts', // barrel files as object assemblers
+          'src/**/definition.declared.augmentation.ts', // side-effect files for module augmentation
+          'src/**/definition.declared.withAugmentation.ts', // barrel files as object augmenters
+          'src/**/core.ts', // 3rd party facades
+        ],
+        reporter: [
+          'json-summary', // Used to generate list of units missing test companions
+        ],
+      },
     },
   }),
 );
diff --git a/vitest/Coverage/Summary/ByFilePath.ts b/vitest/Coverage/Summary/ByFilePath.ts
new file mode 100644
index 000000000..86db365fb
--- /dev/null
+++ b/vitest/Coverage/Summary/ByFilePath.ts
@@ -0,0 +1,18 @@
+import {
+  Schema,
+} from 'effect';
+
+import {
+  Coverage_Summary_ByLanguageConstruct,
+} from './ByLanguageConstruct';
+
+const Coverage_Summary_ByFilePath = Schema.Record({
+  key  : Schema.String,
+  value: Coverage_Summary_ByLanguageConstruct,
+});
+
+type Coverage_Summary_ByFilePath = typeof Coverage_Summary_ByFilePath.Type;
+
+export {
+  Coverage_Summary_ByFilePath,
+};
diff --git a/vitest/Coverage/Summary/ByLanguageConstruct.ts b/vitest/Coverage/Summary/ByLanguageConstruct.ts
new file mode 100644
index 000000000..92e89c655
--- /dev/null
+++ b/vitest/Coverage/Summary/ByLanguageConstruct.ts
@@ -0,0 +1,23 @@
+import {
+  Schema,
+} from 'effect';
+
+import {
+  Coverage_Summary_ByMetric,
+} from './ByMetric';
+
+class Coverage_Summary_ByLanguageConstruct
+  extends Schema.Class<
+    Coverage_Summary_ByLanguageConstruct
+  >(
+    'Coverage_Summary_ByLanguageConstruct',
+  )({
+    lines     : Coverage_Summary_ByMetric,
+    functions : Coverage_Summary_ByMetric,
+    statements: Coverage_Summary_ByMetric,
+    branches  : Coverage_Summary_ByMetric,
+  }) {}
+
+export {
+  Coverage_Summary_ByLanguageConstruct,
+};
diff --git a/vitest/Coverage/Summary/ByMetric.ts b/vitest/Coverage/Summary/ByMetric.ts
new file mode 100644
index 000000000..338d313bc
--- /dev/null
+++ b/vitest/Coverage/Summary/ByMetric.ts
@@ -0,0 +1,19 @@
+import {
+  Schema,
+} from 'effect';
+
+class Coverage_Summary_ByMetric
+  extends Schema.Class<
+    Coverage_Summary_ByMetric
+  >(
+    'Coverage_Summary_ByMetric',
+  )({
+    total  : Schema.Number,
+    covered: Schema.Number,
+    skipped: Schema.Number,
+    pct    : Schema.Number,
+  }) {}
+
+export {
+  Coverage_Summary_ByMetric,
+};
diff --git a/vitest/Coverage/Summary/File/defaultPathRelativeToProjectRoot.ts b/vitest/Coverage/Summary/File/defaultPathRelativeToProjectRoot.ts
new file mode 100644
index 000000000..5af4a7290
--- /dev/null
+++ b/vitest/Coverage/Summary/File/defaultPathRelativeToProjectRoot.ts
@@ -0,0 +1,5 @@
+const Coverage_Summary_File_defaultPathRelativeToProjectRoot = './coverage/coverage-summary.json';
+
+export {
+  Coverage_Summary_File_defaultPathRelativeToProjectRoot,
+};
diff --git a/vitest/Coverage/Summary/File/definition.assembled.members.ts b/vitest/Coverage/Summary/File/definition.assembled.members.ts
new file mode 100644
index 000000000..f1bfc26e8
--- /dev/null
+++ b/vitest/Coverage/Summary/File/definition.assembled.members.ts
@@ -0,0 +1,3 @@
+export {
+  Coverage_Summary_File_find as find,
+} from './find';
diff --git a/vitest/Coverage/Summary/File/definition.assembled.ts b/vitest/Coverage/Summary/File/definition.assembled.ts
new file mode 100644
index 000000000..41864cee7
--- /dev/null
+++ b/vitest/Coverage/Summary/File/definition.assembled.ts
@@ -0,0 +1 @@
+export * as Coverage_Summary_File from './definition.assembled.members.ts';
diff --git a/vitest/Coverage/Summary/File/exports.object.primary.ts b/vitest/Coverage/Summary/File/exports.object.primary.ts
new file mode 100644
index 000000000..8ac7983ac
--- /dev/null
+++ b/vitest/Coverage/Summary/File/exports.object.primary.ts
@@ -0,0 +1 @@
+export * from './definition.assembled.ts';
diff --git a/vitest/Coverage/Summary/File/find.ts b/vitest/Coverage/Summary/File/find.ts
new file mode 100644
index 000000000..8af6c8298
--- /dev/null
+++ b/vitest/Coverage/Summary/File/find.ts
@@ -0,0 +1,35 @@
+import {
+  Effect,
+} from 'effect';
+
+import File from '../../../../@internal/File';
+import FilesystemPath from '../../../../@internal/FilesystemPath';
+
+import {
+  Coverage_Summary_File_defaultPathRelativeToProjectRoot,
+} from './defaultPathRelativeToProjectRoot';
+
+const Coverage_Summary_File_find = (
+  {
+    withRoot: givenProjectRoot,
+    at: givenPathFromSummaryFileToProjectRoot = Coverage_Summary_File_defaultPathRelativeToProjectRoot,
+  }: {
+    withRoot: FilesystemPath;
+    at?: string;
+  },
+): Effect.Effect<FilesystemPath, Error> => Effect.gen(function* () {
+  const pathToCoverageSummary = FilesystemPath.resolved({
+    from: givenProjectRoot,
+    to  : givenPathFromSummaryFileToProjectRoot,
+  });
+
+  if (
+    File.doesExistAt(pathToCoverageSummary)
+  ) return pathToCoverageSummary;
+
+  return yield* Effect.fail(new Error(`No coverage summary file found at ${pathToCoverageSummary.root + pathToCoverageSummary.name}`));
+});
+
+export {
+  Coverage_Summary_File_find,
+};
diff --git a/vitest/Coverage/Summary/File/index.ts b/vitest/Coverage/Summary/File/index.ts
new file mode 100644
index 000000000..70dad59f8
--- /dev/null
+++ b/vitest/Coverage/Summary/File/index.ts
@@ -0,0 +1 @@
+export * from './exports.object.primary.ts';
diff --git a/vitest/Coverage/Summary/FromMixed.ts b/vitest/Coverage/Summary/FromMixed.ts
new file mode 100644
index 000000000..74c998fc6
--- /dev/null
+++ b/vitest/Coverage/Summary/FromMixed.ts
@@ -0,0 +1,39 @@
+import {
+  Schema,
+} from 'effect';
+
+import {
+  Coverage_Summary_Mixed,
+} from './Mixed';
+
+import {
+  Coverage_Summary,
+} from './definition.declared.ts';
+
+const Coverage_Summary_FromMixed = Schema.transform(
+  Coverage_Summary_Mixed.Schema,
+  Coverage_Summary,
+  {
+    decode: (someMixedRecord) => {
+      const {
+        [Coverage_Summary_Mixed.keyForAggregate]: aggregateSummary, // TODO this is missing the "branchTrue" key
+        ...summaryByFile
+      } = someMixedRecord;
+
+      return {
+        aggregate : aggregateSummary,
+        byFilePath: summaryByFile,
+      };
+    },
+    encode: ($0) => {
+      return {
+        [Coverage_Summary_Mixed.keyForAggregate]: $0.aggregate,
+        ...$0.byFilePath,
+      };
+    },
+  },
+);
+
+export {
+  Coverage_Summary_FromMixed,
+};
diff --git a/vitest/Coverage/Summary/Mixed/Schema.ts b/vitest/Coverage/Summary/Mixed/Schema.ts
new file mode 100644
index 000000000..1c35f1d44
--- /dev/null
+++ b/vitest/Coverage/Summary/Mixed/Schema.ts
@@ -0,0 +1,16 @@
+import {
+  Schema,
+} from 'effect';
+
+import {
+  Coverage_Summary_ByLanguageConstruct,
+} from '../ByLanguageConstruct';
+
+const Coverage_Summary_Mixed_Schema = Schema.Record({
+  key  : Schema.String,
+  value: Coverage_Summary_ByLanguageConstruct,
+});
+
+export {
+  Coverage_Summary_Mixed_Schema,
+};
diff --git a/vitest/Coverage/Summary/Mixed/definition.declared.ts b/vitest/Coverage/Summary/Mixed/definition.declared.ts
new file mode 100644
index 000000000..722c1fde9
--- /dev/null
+++ b/vitest/Coverage/Summary/Mixed/definition.declared.ts
@@ -0,0 +1,18 @@
+import {
+  Coverage_Summary_Mixed_Schema,
+} from './Schema';
+
+import {
+  Coverage_Summary_Mixed_keyForAggregate,
+} from './keyForAggregate';
+
+type Coverage_Summary_Mixed = typeof Coverage_Summary_Mixed_Schema.Type;
+
+const Coverage_Summary_Mixed = Object.freeze({
+  Schema         : Coverage_Summary_Mixed_Schema,
+  keyForAggregate: Coverage_Summary_Mixed_keyForAggregate,
+});
+
+export {
+  Coverage_Summary_Mixed,
+};
diff --git a/vitest/Coverage/Summary/Mixed/exports.object.primary.ts b/vitest/Coverage/Summary/Mixed/exports.object.primary.ts
new file mode 100644
index 000000000..0751b4162
--- /dev/null
+++ b/vitest/Coverage/Summary/Mixed/exports.object.primary.ts
@@ -0,0 +1 @@
+export * from './definition.declared.ts';
diff --git a/vitest/Coverage/Summary/Mixed/index.ts b/vitest/Coverage/Summary/Mixed/index.ts
new file mode 100644
index 000000000..70dad59f8
--- /dev/null
+++ b/vitest/Coverage/Summary/Mixed/index.ts
@@ -0,0 +1 @@
+export * from './exports.object.primary.ts';
diff --git a/vitest/Coverage/Summary/Mixed/keyForAggregate.ts b/vitest/Coverage/Summary/Mixed/keyForAggregate.ts
new file mode 100644
index 000000000..114f6b9aa
--- /dev/null
+++ b/vitest/Coverage/Summary/Mixed/keyForAggregate.ts
@@ -0,0 +1,5 @@
+const Coverage_Summary_Mixed_keyForAggregate = 'total';
+
+export {
+  Coverage_Summary_Mixed_keyForAggregate,
+};
diff --git a/vitest/Coverage/Summary/definition.declared.augmentation.ts b/vitest/Coverage/Summary/definition.declared.augmentation.ts
new file mode 100644
index 000000000..3b84ec1e1
--- /dev/null
+++ b/vitest/Coverage/Summary/definition.declared.augmentation.ts
@@ -0,0 +1,41 @@
+import {
+  Coverage_Summary_ByFilePath,
+} from './ByFilePath';
+
+import {
+  Coverage_Summary_ByLanguageConstruct,
+} from './ByLanguageConstruct';
+
+import {
+  Coverage_Summary_ByMetric,
+} from './ByMetric';
+
+import {
+  Coverage_Summary_File,
+} from './File';
+
+import {
+  Coverage_Summary,
+} from './definition.declared.ts';
+
+import {
+  Coverage_Summary_parsedFrom,
+} from './parsedFrom';
+
+Coverage_Summary.parsedFrom /*    */ = Coverage_Summary_parsedFrom;
+Coverage_Summary.File /*          */ = Coverage_Summary_File;
+Coverage_Summary.ByFilePath /*    */ = Coverage_Summary_ByFilePath;
+Coverage_Summary.ByLanguageConstruct = Coverage_Summary_ByLanguageConstruct;
+Coverage_Summary.ByMetric /*      */ = Coverage_Summary_ByMetric;
+
+declare module './definition.declared.ts' {
+  namespace Coverage_Summary {
+    export {
+      Coverage_Summary_parsedFrom /*    */ as parsedFrom,
+      Coverage_Summary_File /*          */ as File,
+      Coverage_Summary_ByFilePath /*    */ as ByFilePath,
+      Coverage_Summary_ByLanguageConstruct as ByLanguageConstruct,
+      Coverage_Summary_ByMetric /*      */ as ByMetric,
+    };
+  }
+}
diff --git a/vitest/Coverage/Summary/definition.declared.ts b/vitest/Coverage/Summary/definition.declared.ts
new file mode 100644
index 000000000..e767c0f62
--- /dev/null
+++ b/vitest/Coverage/Summary/definition.declared.ts
@@ -0,0 +1,25 @@
+import {
+  Schema,
+} from 'effect';
+
+import {
+  Coverage_Summary_ByFilePath,
+} from './ByFilePath';
+
+import {
+  Coverage_Summary_ByLanguageConstruct,
+} from './ByLanguageConstruct';
+
+class Coverage_Summary
+  extends Schema.Class<
+    Coverage_Summary
+  >(
+    'Coverage_Summary',
+  )({
+    aggregate : Coverage_Summary_ByLanguageConstruct,
+    byFilePath: Coverage_Summary_ByFilePath,
+  }) {}
+
+export {
+  Coverage_Summary,
+};
diff --git a/vitest/Coverage/Summary/definition.declared.withAugmentation.ts b/vitest/Coverage/Summary/definition.declared.withAugmentation.ts
new file mode 100644
index 000000000..f11cfa9fa
--- /dev/null
+++ b/vitest/Coverage/Summary/definition.declared.withAugmentation.ts
@@ -0,0 +1,3 @@
+import './definition.declared.augmentation.ts';
+
+export * from './definition.declared.ts';
diff --git a/vitest/Coverage/Summary/exports.object.primary.ts b/vitest/Coverage/Summary/exports.object.primary.ts
new file mode 100644
index 000000000..52e0e7aef
--- /dev/null
+++ b/vitest/Coverage/Summary/exports.object.primary.ts
@@ -0,0 +1 @@
+export * from './definition.declared.withAugmentation.ts';
diff --git a/vitest/Coverage/Summary/index.ts b/vitest/Coverage/Summary/index.ts
new file mode 100644
index 000000000..70dad59f8
--- /dev/null
+++ b/vitest/Coverage/Summary/index.ts
@@ -0,0 +1 @@
+export * from './exports.object.primary.ts';
diff --git a/vitest/Coverage/Summary/parsedFrom.ts b/vitest/Coverage/Summary/parsedFrom.ts
new file mode 100644
index 000000000..1b7a4ca9e
--- /dev/null
+++ b/vitest/Coverage/Summary/parsedFrom.ts
@@ -0,0 +1,36 @@
+import {
+  Effect,
+  Schema,
+} from 'effect';
+
+import File from '../../../@internal/File';
+import type FilesystemPath from '../../../@internal/FilesystemPath';
+
+import {
+  Coverage_Summary_FromMixed,
+} from './FromMixed';
+
+import type {
+  Coverage_Summary,
+} from './definition.declared.ts';
+
+const Coverage_Summary_parsedFrom = (
+  givenPath: FilesystemPath,
+): Effect.Effect<Coverage_Summary, Error> => Effect.gen(function* () {
+  if (
+    givenPath.ext !== '.json'
+  ) return yield* Effect.fail(new Error('Path is not a JSON file'));
+
+  if (
+    !File.doesExistAt(givenPath)
+  ) return yield* Effect.fail(new Error('File does not exist'));
+
+  const fileContentsInJSON = File.contentsReadFrom(givenPath);
+  const decodeCoverageSummaryFrom = Schema.decodeUnknown(Schema.parseJson(Coverage_Summary_FromMixed));
+  const decodedCoverageSummary = yield* decodeCoverageSummaryFrom(fileContentsInJSON);
+  return decodedCoverageSummary;
+});
+
+export {
+  Coverage_Summary_parsedFrom,
+};
diff --git a/vitest/Coverage/definition.assembled.members.ts b/vitest/Coverage/definition.assembled.members.ts
new file mode 100644
index 000000000..e2fcdd921
--- /dev/null
+++ b/vitest/Coverage/definition.assembled.members.ts
@@ -0,0 +1,3 @@
+export {
+  Coverage_Summary as Summary,
+} from './Summary';
diff --git a/vitest/Coverage/definition.assembled.ts b/vitest/Coverage/definition.assembled.ts
new file mode 100644
index 000000000..e65ccbb9b
--- /dev/null
+++ b/vitest/Coverage/definition.assembled.ts
@@ -0,0 +1 @@
+export * as Coverage from './definition.assembled.members.ts';
diff --git a/vitest/Coverage/exports.object.primary.ts b/vitest/Coverage/exports.object.primary.ts
new file mode 100644
index 000000000..8ac7983ac
--- /dev/null
+++ b/vitest/Coverage/exports.object.primary.ts
@@ -0,0 +1 @@
+export * from './definition.assembled.ts';
diff --git a/vitest/Coverage/index.ts b/vitest/Coverage/index.ts
new file mode 100644
index 000000000..70dad59f8
--- /dev/null
+++ b/vitest/Coverage/index.ts
@@ -0,0 +1 @@
+export * from './exports.object.primary.ts';
diff --git a/vitest/TestCompanion/definition.assembled.members.ts b/vitest/TestCompanion/definition.assembled.members.ts
new file mode 100644
index 000000000..90236a8bb
--- /dev/null
+++ b/vitest/TestCompanion/definition.assembled.members.ts
@@ -0,0 +1,15 @@
+export {
+  TestCompanion_extension as extension,
+} from './extension';
+
+export {
+  TestCompanion_preExtensionSuffix as preExtensionSuffix,
+} from './preExtensionSuffix';
+
+export {
+  TestCompanion_pathAssumedFor as pathAssumedFor,
+} from './pathAssumedFor';
+
+export {
+  TestCompanion_doesExistFor as doesExistFor,
+} from './doesExistFor';
diff --git a/vitest/TestCompanion/definition.assembled.ts b/vitest/TestCompanion/definition.assembled.ts
new file mode 100644
index 000000000..b8a35999f
--- /dev/null
+++ b/vitest/TestCompanion/definition.assembled.ts
@@ -0,0 +1 @@
+export * as TestCompanion from './definition.assembled.members.ts';
diff --git a/vitest/TestCompanion/doesExistFor.ts b/vitest/TestCompanion/doesExistFor.ts
new file mode 100644
index 000000000..0c2c59829
--- /dev/null
+++ b/vitest/TestCompanion/doesExistFor.ts
@@ -0,0 +1,21 @@
+import {
+  Effect,
+} from 'effect';
+
+import File from '../../@internal/File';
+import type FilesystemPath from '../../@internal/FilesystemPath';
+
+import {
+  TestCompanion_pathAssumedFor,
+} from './pathAssumedFor';
+
+const TestCompanion_doesExistFor = (
+  givenUnitPath: FilesystemPath,
+): Effect.Effect<boolean, Error> => Effect.gen(function* () {
+  const pathToExpectedTestCompanion = yield* TestCompanion_pathAssumedFor(givenUnitPath);
+  return File.doesExistAt(pathToExpectedTestCompanion);
+});
+
+export {
+  TestCompanion_doesExistFor,
+};
diff --git a/vitest/TestCompanion/exports.object.primary.ts b/vitest/TestCompanion/exports.object.primary.ts
new file mode 100644
index 000000000..8ac7983ac
--- /dev/null
+++ b/vitest/TestCompanion/exports.object.primary.ts
@@ -0,0 +1 @@
+export * from './definition.assembled.ts';
diff --git a/vitest/TestCompanion/extension.ts b/vitest/TestCompanion/extension.ts
new file mode 100644
index 000000000..7eb22f935
--- /dev/null
+++ b/vitest/TestCompanion/extension.ts
@@ -0,0 +1,5 @@
+const TestCompanion_extension = '.ts';
+
+export {
+  TestCompanion_extension,
+};
diff --git a/vitest/TestCompanion/index.ts b/vitest/TestCompanion/index.ts
new file mode 100644
index 000000000..70dad59f8
--- /dev/null
+++ b/vitest/TestCompanion/index.ts
@@ -0,0 +1 @@
+export * from './exports.object.primary.ts';
diff --git a/vitest/TestCompanion/pathAssumedFor.ts b/vitest/TestCompanion/pathAssumedFor.ts
new file mode 100644
index 000000000..ceda2c80d
--- /dev/null
+++ b/vitest/TestCompanion/pathAssumedFor.ts
@@ -0,0 +1,31 @@
+import {
+  Effect,
+} from 'effect';
+
+import FilesystemPath from '../../@internal/FilesystemPath';
+
+import {
+  TestCompanion_extension,
+} from './extension';
+
+import {
+  TestCompanion_preExtensionSuffix,
+} from './preExtensionSuffix';
+
+const TestCompanion_pathAssumedFor = (
+  givenUnit: FilesystemPath,
+): Effect.Effect<FilesystemPath, Error> => Effect.gen(function* () {
+  if (
+    givenUnit.ext !== TestCompanion_extension
+  ) return yield* Effect.fail(new Error('Only TypeScript files are considered for test companions'));
+
+  const potentialTestCompanion = FilesystemPath.from(givenUnit, {
+    name: ($0) => $0 + TestCompanion_preExtensionSuffix,
+  });
+
+  return potentialTestCompanion;
+});
+
+export {
+  TestCompanion_pathAssumedFor,
+};
diff --git a/vitest/TestCompanion/preExtensionSuffix.ts b/vitest/TestCompanion/preExtensionSuffix.ts
new file mode 100644
index 000000000..f69a08afb
--- /dev/null
+++ b/vitest/TestCompanion/preExtensionSuffix.ts
@@ -0,0 +1,5 @@
+const TestCompanion_preExtensionSuffix = '.test';
+
+export {
+  TestCompanion_preExtensionSuffix,
+};
diff --git a/vitest/TestableUnit/allThoseMissingCompanionAccordingTo.ts b/vitest/TestableUnit/allThoseMissingCompanionAccordingTo.ts
new file mode 100644
index 000000000..bd22ddcae
--- /dev/null
+++ b/vitest/TestableUnit/allThoseMissingCompanionAccordingTo.ts
@@ -0,0 +1,32 @@
+import {
+  Effect,
+} from 'effect';
+
+import FilesystemPath from '../../@internal/FilesystemPath';
+
+import type {
+  Coverage,
+} from '../Coverage';
+
+import {
+  TestCompanion,
+} from '../TestCompanion';
+
+const TestableUnit_allThoseMissingCompanionAccordingTo = (
+  givenSummary: Coverage.Summary,
+): FilesystemPath[] => {
+  const pathsToUnitsThatHaveNoTestImplementation = Object.entries(givenSummary.byFilePath)
+    .filter(([, eachMetric]) => {
+      return (0 === eachMetric.functions.pct)
+        || (0 === eachMetric.statements.pct);
+    })
+    .map(([$0]) => $0);
+
+  const unitsThatHaveNoTestImplementation = pathsToUnitsThatHaveNoTestImplementation.map(FilesystemPath.parsedFrom);
+  const unitsThatHaveNoTestCompanion = unitsThatHaveNoTestImplementation.filter(($0) => !TestCompanion.doesExistFor($0).pipe(Effect.runSync));
+  return unitsThatHaveNoTestCompanion;
+};
+
+export {
+  TestableUnit_allThoseMissingCompanionAccordingTo,
+};
diff --git a/vitest/TestableUnit/definition.assembled.members.ts b/vitest/TestableUnit/definition.assembled.members.ts
new file mode 100644
index 000000000..6c64c971b
--- /dev/null
+++ b/vitest/TestableUnit/definition.assembled.members.ts
@@ -0,0 +1,7 @@
+export {
+  TestableUnit_getAllThatAreMissingTestCompanion as getAllThatAreMissingTestCompanion,
+} from './getAllThatAreMissingTestCompanion';
+
+export {
+  TestableUnit_allThoseMissingCompanionAccordingTo as allThoseMissingCompanionAccordingTo,
+} from './allThoseMissingCompanionAccordingTo';
diff --git a/vitest/TestableUnit/definition.assembled.ts b/vitest/TestableUnit/definition.assembled.ts
new file mode 100644
index 000000000..b9ce8af04
--- /dev/null
+++ b/vitest/TestableUnit/definition.assembled.ts
@@ -0,0 +1 @@
+export * as TestableUnit from './definition.assembled.members.ts';
diff --git a/vitest/TestableUnit/exports.object.primary.ts b/vitest/TestableUnit/exports.object.primary.ts
new file mode 100644
index 000000000..8ac7983ac
--- /dev/null
+++ b/vitest/TestableUnit/exports.object.primary.ts
@@ -0,0 +1 @@
+export * from './definition.assembled.ts';
diff --git a/vitest/TestableUnit/getAllThatAreMissingTestCompanion.ts b/vitest/TestableUnit/getAllThatAreMissingTestCompanion.ts
new file mode 100644
index 000000000..f0ab35cfd
--- /dev/null
+++ b/vitest/TestableUnit/getAllThatAreMissingTestCompanion.ts
@@ -0,0 +1,38 @@
+import {
+  Effect,
+} from 'effect';
+
+import {
+  toPath,
+} from '../../@internal/File';
+
+import type FilesystemPath from '../../@internal/FilesystemPath';
+
+import {
+  Coverage,
+} from '../Coverage';
+
+import {
+  TestableUnit_allThoseMissingCompanionAccordingTo,
+} from './allThoseMissingCompanionAccordingTo';
+
+const TestableUnit_getAllThatAreMissingTestCompanion: Effect.Effect<FilesystemPath[], Error> = Effect.gen(function* () {
+  const pathFromCurrentModuleToProjectRoot = '../../../';
+
+  const projectRoot = toPath(new URL(
+    pathFromCurrentModuleToProjectRoot,
+    import.meta.url,
+  ));
+
+  const fileFoundForCoverageSummary = yield* Coverage.Summary.File.find({
+    withRoot: projectRoot,
+  });
+
+  const parsedCoverageSummary = yield* Coverage.Summary.parsedFrom(fileFoundForCoverageSummary);
+
+  return TestableUnit_allThoseMissingCompanionAccordingTo(parsedCoverageSummary);
+});
+
+export {
+  TestableUnit_getAllThatAreMissingTestCompanion,
+};
diff --git a/vitest/TestableUnit/index.ts b/vitest/TestableUnit/index.ts
new file mode 100644
index 000000000..70dad59f8
--- /dev/null
+++ b/vitest/TestableUnit/index.ts
@@ -0,0 +1 @@
+export * from './exports.object.primary.ts';
diff --git a/vitest/ensure-all-units-have-test-companion.ts b/vitest/ensure-all-units-have-test-companion.ts
new file mode 100644
index 000000000..b10aee652
--- /dev/null
+++ b/vitest/ensure-all-units-have-test-companion.ts
@@ -0,0 +1,43 @@
+import {
+  Effect,
+} from 'effect';
+
+import {
+  toPath,
+} from '../@internal/File';
+
+import {
+  serialized,
+} from '../@internal/FilesystemPath';
+
+import {
+  TestableUnit,
+} from './TestableUnit';
+
+const unitsWithoutCompanions = TestableUnit.getAllThatAreMissingTestCompanion.pipe(
+  Effect.mapError((caughtFailure) => {
+    console.error(caughtFailure);
+    process.exit(1);
+  }),
+  Effect.runSync,
+);
+
+if (
+  unitsWithoutCompanions.length === 0
+) process.exit(0);
+
+const pathFromCurrentModuleToProjectRoot = '../';
+
+const projectRoot = toPath(new URL(
+  pathFromCurrentModuleToProjectRoot,
+  import.meta.url,
+));
+
+const absolutePathToProjectRoot = serialized(projectRoot);
+
+const serializedUnitsWithoutCompanions = unitsWithoutCompanions
+  .map(($0) => serialized($0).replace(absolutePathToProjectRoot, ''))
+  .join('\n');
+
+console.error(`The following ${unitsWithoutCompanions.length.toString()} unit(s) have no test companion:\n${serializedUnitsWithoutCompanions}`);
+process.exit(1);