feat(pipes): add slice pipe that supports start and end indexes

modules/angular2/test/pipes/slice_pipe_spec.ts

@@ -0,0 +1,75 @@
+import {ddescribe, describe, it, iit, xit, expect, beforeEach, afterEach} from 'angular2/test_lib';
+
+import {SlicePipe} from 'angular2/pipes';
+
+export function main() {
+  describe("SlicePipe", () => {
+    var list;
+    var str;
+    var pipe;
+
+    beforeEach(() => {
+      list = [1, 2, 3, 4, 5];
+      str = 'tuvwxyz';
+      pipe = new SlicePipe();
+    });
+
+    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 all items after START index when START is positive and END is omitted',
+         () => {
+           expect(pipe.transform(list, [3])).toEqual([4, 5]);
+           expect(pipe.transform(str, [3])).toEqual('wxyz');
+         });
+
+      it('should return last START items when START is negative and END is omitted', () => {
+        expect(pipe.transform(list, [-3])).toEqual([3, 4, 5]);
+        expect(pipe.transform(str, [-3])).toEqual('xyz');
+      });
+
+      it('should return all items between START and END index when START and END are positive',
+         () => {
+           expect(pipe.transform(list, [1, 3])).toEqual([2, 3]);
+           expect(pipe.transform(str, [1, 3])).toEqual('uv');
+         });
+
+      it('should return all items between START and END from the end when START and END are negative',
+         () => {
+           expect(pipe.transform(list, [-4, -2])).toEqual([2, 3]);
+           expect(pipe.transform(str, [-4, -2])).toEqual('wx');
+         });
+
+      it('should return an empty value if START is greater than END', () => {
+        expect(pipe.transform(list, [4, 2])).toEqual([]);
+        expect(pipe.transform(str, [4, 2])).toEqual('');
+      });
+
+      it('should return an empty value if START greater than input length', () => {
+        expect(pipe.transform(list, [99])).toEqual([]);
+        expect(pipe.transform(str, [99])).toEqual('');
+      });
+
+      it('should return entire input if START is negative and greater than input length', () => {
+        expect(pipe.transform(list, [-99])).toEqual([1, 2, 3, 4, 5]);
+        expect(pipe.transform(str, [-99])).toEqual('tuvwxyz');
+      });
+
+      it('should not modify the input list', () => {
+        expect(pipe.transform(list, [2])).toEqual([3, 4, 5]);
+        expect(list).toEqual([1, 2, 3, 4, 5]);
+      });
+
+    });
+
+  });
+}