LibJS: Multiple 'default' clauses in switch statement are a syntax error

Author: https://github.com/linusg
Commit: 2dbea60fe2
Pull-request: https://github.com/SerenityOS/serenity/pull/3795

Libraries/LibJS/Tests/switch-basic.js

@@ -68,3 +68,11 @@ describe("basic switch tests", () => {
         expect(i).toBe(5);
     });
 });
+
+describe("errors", () => {
+    test("syntax errors", () => {
+        expect("switch () {}").not.toEval();
+        expect("switch (foo) { bar }").not.toEval();
+        expect("switch (foo) { default: default: }").not.toEval();
+    });
+});