LibJS: Add Proxy [[Call]] and [[Construct]] tests

Author: https://github.com/mattco98
Commit: https://github.com/SerenityOS/serenity/commit/19411e22d0d
Pull-request: https://github.com/SerenityOS/serenity/pull/2630
Issue: https://github.com/SerenityOS/serenity/issues/2624
Reviewed-by: https://github.com/awesomekling

Libraries/LibJS/Tests/Proxy.handler-apply.js

@@ -0,0 +1,39 @@
+load("test-common.js");
+
+try {
+    let p = new Proxy(() => 5, { apply: null });
+    assert(p() === 5);
+    let p = new Proxy(() => 5, { apply: undefined });
+    assert(p() === 5);
+    let p = new Proxy(() => 5, {});
+    assert(p() === 5);
+
+    const f = (a, b) => a + b;
+    const handler = {
+        apply(target, this_, arguments) {
+            assert(target === f);
+            assert(this_ === handler);
+            if (arguments[2])
+                return arguments[0] * arguments[1];
+            return f(...arguments);
+        },
+    };
+    p = new Proxy(f, handler);
+
+    assert(p(2, 4) === 6);
+    assert(p(2, 4, true) === 8);
+
+    // Invariants
+    [{}, [], new Proxy({}, {})].forEach(item => {
+        assertThrowsError(() => {
+            new Proxy(item, {})();
+        }, {
+            error: TypeError,
+            message: "[object ProxyObject] is not a function",
+        });
+    });
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}

Libraries/LibJS/Tests/Proxy.handler-construct.js

@@ -0,0 +1,43 @@
+load("test-common.js");
+
+try {
+    let p = new Proxy(function() { this.x = 5; }, { construct: null });
+    assert((new p).x === 5);
+    let p = new Proxy(function() { this.x = 5; }, { construct: undefined });
+    assert((new p).x === 5);
+    let p = new Proxy(function() { this.x = 5; }, {});
+    assert((new p).x === 5);
+
+    function f(value) {
+        this.x = value;
+    }
+
+    let p;
+    const handler = {
+        construct(target, arguments, newTarget) {
+            assert(target === f);
+            assert(newTarget === p);
+            if (arguments[1])
+                return Reflect.construct(target, [arguments[0] * 2], newTarget);
+            return Reflect.construct(target, arguments, newTarget);
+        },
+    };
+    p = new Proxy(f, handler);
+
+    assert(new p(15).x === 15);
+    assert(new p(15, true).x === 30);
+
+    // Invariants
+    [{}, [], new Proxy({}, {})].forEach(item => {
+        assertThrowsError(() => {
+            new (new Proxy(item, {}));
+        }, {
+            error: TypeError,
+            message: "[object ProxyObject] is not a constructor",
+        });
+    });
+
+    console.log("PASS");
+} catch (e) {
+    console.log("FAIL: " + e);
+}