Merge pull request #395 from olafurpg/array-eq

Improve error message when comparing arrays with same elements
scalameta · Jul 26, 2021 · 0354373 · 0354373
2 parents de84d57 + 02c092f
commit 0354373
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diff --git a/munit/shared/src/main/scala/munit/Assertions.scala b/munit/shared/src/main/scala/munit/Assertions.scala
@@ -116,6 +116,28 @@ trait Assertions extends MacroCompat.CompileErrorMacro {
   )(implicit loc: Location, ev: B <:< A): Unit = {
     StackTraces.dropInside {
       if (obtained != expected) {
+
+        (obtained, expected) match {
+          case (a: Array[_], b: Array[_]) if a.sameElements(b) =>
+            // Special-case error message when comparing arrays. See
+            // https://github.com/scalameta/munit/pull/393 and
+            // https://github.com/scalameta/munit/issues/339 for a related
+            // discussion on how MUnit should handle array comparisons.  Other
+            // testing frameworks have special cases for arrays so the
+            // comparison succeeds as long as `sameElements()` returns true.
+            // MUnit chooses instead to fail the test with a custom error
+            // message because arrays have reference equality, for better or
+            // worse, and we should not hide that fact from our users.
+            failComparison(
+              "arrays have the same elements but different reference equality. " +
+                "Convert the arrays to a non-Array collection if you intend to assert the two arrays have the same elements. " +
+                "For example, `assertEquals(a.toSeq, b.toSeq)",
+              obtained,
+              expected
+            )
+          case _ =>
+        }
+
         Diffs.assertNoDiff(
           munitPrint(obtained),
           munitPrint(expected),

diff --git a/tests/shared/src/test/scala/munit/AssertionsSuite.scala b/tests/shared/src/test/scala/munit/AssertionsSuite.scala
@@ -58,4 +58,14 @@ class AssertionsSuite extends BaseSuite {
          |""".stripMargin
     )
   }
+  test("array-sameElements") {
+    val e = intercept[ComparisonFailException] {
+      assertEquals(Array(1, 2), Array(1, 2))
+    }
+    assert(
+      clue(e).getMessage.contains(
+        "arrays have the same elements but different reference equality. Convert the arrays to a non-Array collection if you intend to assert the two arrays have the same elements. For example, `assertEquals(a.toSeq, b.toSeq)"
+      )
+    )
+  }
 }