Allow explicit_write in tests

Author: smoelius

clippy_lints/src/explicit_write.rs

@@ -1,7 +1,7 @@
 use clippy_utils::diagnostics::span_lint_and_sugg;
 use clippy_utils::macros::{FormatArgsStorage, format_args_inputs_span};
 use clippy_utils::source::snippet_with_applicability;
-use clippy_utils::{is_expn_of, path_def_id, sym};
+use clippy_utils::{is_expn_of, is_in_test, path_def_id, sym};
 use rustc_errors::Applicability;
 use rustc_hir::def::Res;
 use rustc_hir::{BindingMode, Block, BlockCheckMode, Expr, ExprKind, Node, PatKind, QPath, Stmt, StmtKind};
@@ -52,6 +52,9 @@ impl_lint_pass!(ExplicitWrite => [EXPLICIT_WRITE]);
 
 impl<'tcx> LateLintPass<'tcx> for ExplicitWrite {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
+        if is_in_test(cx.tcx, expr.hir_id) {
+            return;
+        }
         // match call to unwrap
         if let ExprKind::MethodCall(unwrap_fun, write_call, [], _) = expr.kind
             && unwrap_fun.ident.name == sym::unwrap

tests/ui/explicit_write_in_test.rs

@@ -0,0 +1,9 @@
+//@ check-pass
+#![warn(clippy::explicit_write)]
+
+#[test]
+fn test() {
+    use std::io::Write;
+    writeln!(std::io::stderr(), "I am an explicit write.").unwrap();
+    eprintln!("I am not an explicit write.");
+}