LibJS: Implement Iterator.prototype.drop

Userland/Libraries/LibJS/Tests/builtins/Iterator/Iterator.prototype.drop.js

@@ -0,0 +1,118 @@
+describe("errors", () => {
+    test("called with non-numeric object", () => {
+        expect(() => {
+            Iterator.prototype.drop(Symbol.hasInstance);
+        }).toThrowWithMessage(TypeError, "Cannot convert symbol to number");
+    });
+
+    test("called with invalid numbers", () => {
+        expect(() => {
+            Iterator.prototype.drop(NaN);
+        }).toThrowWithMessage(RangeError, "limit must not be NaN");
+
+        expect(() => {
+            Iterator.prototype.drop(-1);
+        }).toThrowWithMessage(RangeError, "limit must not be negative");
+    });
+
+    test("iterator's next method throws", () => {
+        function TestError() {}
+
+        class TestIterator extends Iterator {
+            next() {
+                throw new TestError();
+            }
+        }
+
+        expect(() => {
+            const iterator = new TestIterator().drop(1);
+            iterator.next();
+        }).toThrow(TestError);
+    });
+
+    test("value returned by iterator's next method throws", () => {
+        function TestError() {}
+
+        class TestIterator extends Iterator {
+            next() {
+                return {
+                    done: false,
+                    get value() {
+                        throw new TestError();
+                    },
+                };
+            }
+        }
+
+        expect(() => {
+            const iterator = new TestIterator().drop(1);
+            iterator.next();
+        }).toThrow(TestError);
+    });
+});
+
+describe("normal behavior", () => {
+    test("length is 1", () => {
+        expect(Iterator.prototype.drop).toHaveLength(1);
+    });
+
+    test("drop zero values", () => {
+        function* generator() {
+            yield "a";
+            yield "b";
+        }
+
+        const iterator = generator().drop(0);
+
+        let value = iterator.next();
+        expect(value.value).toBe("a");
+        expect(value.done).toBeFalse();
+
+        value = iterator.next();
+        expect(value.value).toBe("b");
+        expect(value.done).toBeFalse();
+
+        value = iterator.next();
+        expect(value.value).toBeUndefined();
+        expect(value.done).toBeTrue();
+    });
+
+    test("drop fewer than the number of values", () => {
+        function* generator() {
+            yield "a";
+            yield "b";
+            yield "c";
+        }
+
+        const iterator = generator().drop(1);
+
+        let value = iterator.next();
+        expect(value.value).toBe("b");
+        expect(value.done).toBeFalse();
+
+        value = iterator.next();
+        expect(value.value).toBe("c");
+        expect(value.done).toBeFalse();
+
+        value = iterator.next();
+        expect(value.value).toBeUndefined();
+        expect(value.done).toBeTrue();
+    });
+
+    test("drop more than the number of values", () => {
+        function* generator() {
+            yield "a";
+            yield "b";
+        }
+
+        const iterator = generator().drop(Infinity);
+
+        let value = iterator.next();
+        expect(value.value).toBeUndefined();
+        expect(value.done).toBeTrue();
+
+        value = iterator.next();
+        expect(value.value).toBeUndefined();
+        expect(value.done).toBeTrue();
+    });
+});