add tests for reducers

tests/reducers/windows.test.js

+import reducer from '../../reducers/windows';
+import ActionTypes from '../../action-types';
+
+describe('windows reducer', () => {
+  it('should handle ADD_WINDOW', () => {
+    expect(reducer([], {
+      type: ActionTypes.ADD_WINDOW,
+    })).toEqual([
+      {},
+    ]);
+  });
+  it('should handle REMOVE_WINDOW', () => {
+    expect(reducer([
+      {
+        id: 'abc123',
+      },
+    ], {
+      type: ActionTypes.REMOVE_WINDOW,
+      windowId: 'abc123',
+    })).toEqual([]);
+  });
+  it('should handle NEXT_CANVAS', () => {
+    expect(reducer([
+      {
+        id: 'abc123',
+        canvasIndex: 1,
+      },
+    ], {
+      type: ActionTypes.NEXT_CANVAS,
+      windowId: 'abc123',
+    })).toEqual([
+      {
+        id: 'abc123',
+        canvasIndex: 2,
+      },
+    ]);
+  });
+  it('should handle PREVIOUS_CANVAS', () => {
+    expect(reducer([
+      {
+        id: 'abc123',
+        canvasIndex: 4,
+      },
+    ], {
+      type: ActionTypes.PREVIOUS_CANVAS,
+      windowId: 'abc123',
+    })).toEqual([
+      {
+        id: 'abc123',
+        canvasIndex: 3,
+      },
+    ]);
+  });
+});

tests/reducers/workspace.test.js

+import reducer from '../../reducers/workspace';
+import ActionTypes from '../../action-types';
+
+describe('workspace reducer', () => {
+  it('should handle FOCUS_WINDOW', () => {
+    expect(reducer([], {
+      type: ActionTypes.FOCUS_WINDOW,
+      windowId: 'abc123',
+    })).toEqual({
+      focusedWindowId: 'abc123',
+    });
+  });
+});