Classify empty_test as suspicious

Empty test functions pass without exercising behaviour and can create
a false sense of coverage. Classify the lint as suspicious and document
a concrete assertion-based replacement.

Author: willwang-io

clippy_lints/src/empty_test.rs

@@ -10,18 +10,32 @@ declare_clippy_lint! {
     /// ### What it does
     /// Checks for test functions with an empty body.
     ///
-    /// ### Why restrict this?
-    /// Empty tests do not verify behavior. However, they can serve as temporary placeholders while
-    /// a test is being developed.
+    /// ### Why is this bad?
+    /// Empty tests pass automatically without asserting any behavior. They often represent
+    /// unfinished work or forgotten stubs, giving a false sense of completeness without
+    /// adding any coverage to the code
     ///
     /// ### Example
     /// ```no_run
+    /// fn add(left: i32, right: i32) -> i32 {
+    ///     left + right
+    /// }
+    ///
     /// #[test]
-    /// fn empty_test() {}
+    /// fn adds_numbers() {}
     /// ```
     ///
-    /// Remove the test if it is no longer needed, or add assertions that exercise the behavior it
-    /// is intended to test.
+    /// Use instead:
+    /// ```no_run
+    /// fn add(left: i32, right: i32) -> i32 {
+    ///     left + right
+    /// }
+    ///
+    /// #[test]
+    /// fn adds_numbers() {
+    ///     assert_eq!(add(1, 2), 3);
+    /// }
+    /// ```
     #[clippy::version = "1.100.0"]
     pub EMPTY_TEST,
     restriction,
@@ -40,9 +54,11 @@ impl LateLintPass<'_> for EmptyTest {
         span: Span,
         fn_def_id: LocalDefId,
     ) {
-        if matches!(kind, FnKind::ItemFn(..))
+        if let ExprKind::Block(block, _) = body.value.kind
+            && block.stmts.is_empty()
+            && block.expr.is_none()
+            && matches!(kind, FnKind::ItemFn(..))
             && is_test_function(cx.tcx, fn_def_id)
-            && matches!(body.value.kind, ExprKind::Block(block, _) if block.stmts.is_empty() && block.expr.is_none())
         {
             span_lint(cx, EMPTY_TEST, span, "empty test function");
         }