update docs

docs/step2-08/exercise/src/reducers/pureFunctions.spec.ts

@@ -0,0 +1,29 @@
+import { addTodo, complete } from './pureFunctions';
+import { Store } from '../store';
+
+describe('TodoApp reducers', () => {
+  it('can add an item', () => {
+    const state = <Store['todos']>{};
+
+    const newState = addTodo(state, '0', 'item1');
+
+    const keys = Object.keys(newState);
+
+    expect(newState).not.toBe(state);
+    expect(keys.length).toBe(1);
+    expect(newState[keys[0]].label).toBe('item1');
+    expect(newState[keys[0]].completed).toBeFalsy();
+  });
+
+  it('can complete an item', () => {
+    const state = <Store['todos']>{};
+
+    let newState = addTodo(state, '0', 'item1');
+
+    const key = Object.keys(newState)[0];
+
+    newState = complete(newState, key);
+
+    expect(newState[key].completed).toBeTruthy();
+  });
+});