feat(pipes): add limitTo pipe

modules/angular2/test/change_detection/pipes/limit_to_pipe_spec.ts

@@ -0,0 +1,57 @@
+import {ddescribe, describe, it, iit, xit, expect, beforeEach, afterEach} from 'angular2/test_lib';
+
+import {LimitToPipe} from 'angular2/src/change_detection/pipes/limit_to_pipe';
+
+export function main() {
+  describe("LimitToPipe", () => {
+    var list;
+    var str;
+    var pipe;
+
+    beforeEach(() => {
+      list = [1, 2, 3, 4, 5];
+      str = 'tuvwxyz';
+      pipe = new LimitToPipe();
+    });
+
+    describe("supports", () => {
+      it("should support strings", () => { expect(pipe.supports(str)).toBe(true); });
+      it("should support lists", () => { expect(pipe.supports(list)).toBe(true); });
+
+      it("should not support other objects", () => {
+        expect(pipe.supports(new Object())).toBe(false);
+        expect(pipe.supports(null)).toBe(false);
+      });
+    });
+
+    describe("transform", () => {
+
+      it('should return the first X items when X is positive', () => {
+        expect(pipe.transform(list, [3])).toEqual([1, 2, 3]);
+        expect(pipe.transform(str, [3])).toEqual('tuv');
+      });
+
+      it('should return the last X items when X is negative', () => {
+        expect(pipe.transform(list, [-3])).toEqual([3, 4, 5]);
+        expect(pipe.transform(str, [-3])).toEqual('xyz');
+      });
+
+      it('should return a copy of input array if X is exceeds array length', () => {
+        expect(pipe.transform(list, [20])).toEqual(list);
+        expect(pipe.transform(list, [-20])).toEqual(list);
+      });
+
+      it('should return the entire string if X exceeds input length', () => {
+        expect(pipe.transform(str, [20])).toEqual(str);
+        expect(pipe.transform(str, [-20])).toEqual(str);
+      });
+
+      it('should not modify the input list', () => {
+        expect(pipe.transform(list, [3])).toEqual([1, 2, 3]);
+        expect(list).toEqual([1, 2, 3, 4, 5]);
+      });
+
+    });
+
+  });
+}