State is shared between tests, causes tests to fail

[spatialillusions]

I did run into a problem yesterday where I found that the state of objects are shared between tests, and this can cause tests to fail. I made a minimal example to illustrate this.

Create the following files:

data.js

var dataObject = {
  data: [],
  addData: function(d) {
    this.data.push(d);
    return this.data.length;
  }
};
export { dataObject };

1.test.js

import { dataObject } from "./data";

export default {
  "add one data element": [dataObject.addData(5), 1]
};

2.test.js

import { dataObject } from "./data";

export default {
  "add one data element": [dataObject.addData(5), 1]
};

Note that the two tests are exactly the same test

When I run the tests, test 1 will pass and test 2 will fail, because it turns out that the dataObject is shared between them and the environment is not reset between tests.

 PASS  1.test.js
  ✓ add one data element

 FAIL  2.test.js
  ✕ add one data element

 FAIL  2.test.js

  ● add one data element

    encountered 2 but expected 1

Expected result
Tests are run independent of each other and changes you do in one test should not effect the result in another test.

Please let me know if there is anything I can do in my tests, or anything I can help out with in tead to solve this.

[okwolf]

Tead is intended for testing purely functional code and is allergic to shared mutable state. One might argue such things are a code smell for tests since it can cause one test to adversely affect others. Some test libraries hack around this by running each test in a fresh environment, but with Tead you will need to explicitly do this yourself.

Each test case should create all the test data it needs from scratch using helper functions as needed. Perhaps the docs could be enhanced to cover this?

[spatialillusions]

Solved it by adding a reset method to my object that resets it to the default state. Do you want me to close the issue, or should we keep it open util you updated the documentation?

[okwolf]

If you’re on board with updating the docs then so am I. Let’s keep this open for that.