assertNever no longer crashes on string input (#29764)

src/testRunner/unittests/asserts.ts

@@ -5,5 +5,8 @@ namespace ts {
             assert.throws(() => assert.deepEqual(createNodeArray([], /*hasTrailingComma*/ true), createNodeArray([], /*hasTrailingComma*/ false)));
             assert.deepEqual(createNodeArray([createIdentifier("A")], /*hasTrailingComma*/ true), createNodeArray([createIdentifier("A")], /*hasTrailingComma*/ true));
         });
+        it("assertNever on string has correct error", () => {
+            assert.throws(() => Debug.assertNever("hi" as never), "Debug Failure. Illegal value: \"hi\"");
+        });
     });
 }