LibJS: Convert all remaining non-Array tests to the new system :)

Author: https://github.com/mattco98
Commit: 15de2eda2b
Pull-request: https://github.com/SerenityOS/serenity/pull/2689
Reviewed-by: https://github.com/linusg

Libraries/LibJS/Tests/loops/for-basic.js

@@ -1,24 +1,15 @@
-load("test-common.js");
-
-try {
-  var a = [];
-  for (var i = 0; i < 3; ++i) {
+test("basic functionality", () => {
+  let a = [];
+  for (let i = 0; i < 3; ++i) {
     a.push(i);
   }
-  assert(a.length === 3);
-  assert(a[0] === 0);
-  assert(a[1] === 1);
-  assert(a[2] === 2);
+  expect(a).toEqual([0, 1, 2]);
+});
 
-  for (; a.length < 6; ) {
+test("only condition", () => {
+  let a = [];
+  for (; a.length < 3; ) {
     a.push("x");
   }
-  assert(a.length === 6);
-  assert(a[3] === "x");
-  assert(a[4] === "x");
-  assert(a[5] === "x");
-
-  console.log("PASS");
-} catch (e) {
-  console.log("FAIL: " + e);
-}
+  expect(a).toEqual(["x", "x", "x"]);
+});