diff --git a/src/reducers/hover.js b/src/reducers/hover.js
index 0c4353b0..2a3e31ee 100644
--- a/src/reducers/hover.js
+++ b/src/reducers/hover.js
@@ -1,3 +1,4 @@
+import paper from 'paper';
 import log from '../log/log';
 
 const CHANGE_HOVERED = 'scratch-paint/hover/CHANGE_HOVERED';
@@ -7,7 +8,8 @@ const reducer = function (state, action) {
     if (typeof state === 'undefined') state = initialState;
     switch (action.type) {
     case CHANGE_HOVERED:
-        if (typeof action.hoveredItem === 'undefined') {
+        if (typeof action.hoveredItem === 'undefined' ||
+                (action.hoveredItem !== null && !(action.hoveredItem instanceof paper.Item))) {
             log.warn(`Hovered item should not be set to undefined. Use null.`);
             return state;
         }
diff --git a/test/unit/components/select-mode.test.jsx b/test/unit/components/select-mode.test.jsx
new file mode 100644
index 00000000..3ec1ba29
--- /dev/null
+++ b/test/unit/components/select-mode.test.jsx
@@ -0,0 +1,15 @@
+/* eslint-env jest */
+import React from 'react'; // eslint-disable-line no-unused-vars
+import {shallow} from 'enzyme';
+import SelectModeComponent from '../../../src/components/select-mode.jsx'; // eslint-disable-line no-unused-vars
+
+describe('SelectModeComponent', () => {
+    test('triggers callback when clicked', () => {
+        const onClick = jest.fn();
+        const componentShallowWrapper = shallow(
+            <SelectModeComponent onMouseDown={onClick}/>
+        );
+        componentShallowWrapper.simulate('click');
+        expect(onClick).toHaveBeenCalled();
+    });
+});
diff --git a/test/unit/hover-reducer.test.js b/test/unit/hover-reducer.test.js
new file mode 100644
index 00000000..b8c63cd0
--- /dev/null
+++ b/test/unit/hover-reducer.test.js
@@ -0,0 +1,40 @@
+/* eslint-env jest */
+import paper from 'paper';
+import reducer from '../../src/reducers/hover';
+import {clearHoveredItem, setHoveredItem} from '../../src/reducers/hover';
+
+beforeEach(() => {
+    paper.setup();
+});
+
+test('initialState', () => {
+    let defaultState;
+    expect(reducer(defaultState /* state */, {type: 'anything'} /* action */)).toBeNull();
+});
+
+test('setHoveredItem', () => {
+    let defaultState;
+    const item1 = new paper.Path();
+    const item2 = new paper.Path();
+    expect(reducer(defaultState /* state */, setHoveredItem(item1) /* action */)).toBe(item1);
+    expect(reducer(item1 /* state */, setHoveredItem(item2) /* action */)).toBe(item2);
+});
+
+test('clearHoveredItem', () => {
+    let defaultState;
+    const item = new paper.Path();
+    expect(reducer(defaultState /* state */, clearHoveredItem() /* action */)).toBeNull();
+    expect(reducer(item /* state */, clearHoveredItem() /* action */)).toBeNull();
+});
+
+test('invalidSetHoveredItem', () => {
+    let defaultState;
+    const item = new paper.Path();
+    const nonItem = {random: 'object'};
+    let undef;
+    expect(reducer(defaultState /* state */, setHoveredItem(nonItem) /* action */)).toBeNull();
+    expect(reducer(item /* state */, setHoveredItem(nonItem) /* action */))
+        .toBe(item);
+    expect(reducer(item /* state */, setHoveredItem(undef) /* action */))
+        .toBe(item);
+});