diff --git a/superset/assets/javascripts/components/Timer.jsx b/superset/assets/javascripts/components/Timer.jsx
index f108e4ce1b21d..b221859d196e3 100644
--- a/superset/assets/javascripts/components/Timer.jsx
+++ b/superset/assets/javascripts/components/Timer.jsx
@@ -2,12 +2,28 @@ import React from 'react';
 import PropTypes from 'prop-types';
 import { now, fDuration } from '../modules/dates';
 
-class Timer extends React.PureComponent {
+const propTypes = {
+  endTime: PropTypes.number,
+  isRunning: PropTypes.bool.isRequired,
+  startTime: PropTypes.number,
+  status: PropTypes.string,
+  style: PropTypes.object,
+};
+
+const defaultProps = {
+  endTime: null,
+  startTime: null,
+  status: 'success',
+  style: null,
+};
+
+export default class Timer extends React.PureComponent {
   constructor(props) {
     super(props);
     this.state = {
       clockStr: '',
     };
+    this.stopwatch = this.stopwatch.bind(this);
   }
   componentWillMount() {
     this.startTimer();
@@ -16,13 +32,12 @@ class Timer extends React.PureComponent {
     this.stopTimer();
   }
   startTimer() {
-    if (!(this.timer)) {
-      this.timer = setInterval(this.stopwatch.bind(this), 30);
+    if (!this.timer) {
+      this.timer = setInterval(this.stopwatch, 30);
     }
   }
   stopTimer() {
-    clearInterval(this.timer);
-    this.timer = null;
+    this.timer = clearInterval(this.timer);
   }
   stopwatch() {
     if (this.props && this.props.startTime) {
@@ -54,19 +69,6 @@ class Timer extends React.PureComponent {
     return timerSpan;
   }
 }
-Timer.propTypes = {
-  startTime: PropTypes.number,
-  endTime: PropTypes.number,
-  isRunning: PropTypes.bool.isRequired,
-  status: PropTypes.string,
-  style: PropTypes.object,
-};
-
-Timer.defaultProps = {
-  startTime: null,
-  endTime: null,
-  status: 'success',
-  style: null,
-};
 
-export default Timer;
+Timer.propTypes = propTypes;
+Timer.defaultProps = defaultProps;
diff --git a/superset/assets/spec/javascripts/sqllab/Timer_spec.jsx b/superset/assets/spec/javascripts/sqllab/Timer_spec.jsx
index 9bad34c32ee7b..21a8a4fb3d442 100644
--- a/superset/assets/spec/javascripts/sqllab/Timer_spec.jsx
+++ b/superset/assets/spec/javascripts/sqllab/Timer_spec.jsx
@@ -1,6 +1,6 @@
 import React from 'react';
-import { shallow } from 'enzyme';
-import { describe, it } from 'mocha';
+import { mount } from 'enzyme';
+import { describe, it, beforeEach } from 'mocha';
 import { expect } from 'chai';
 
 import Timer from '../../../javascripts/components/Timer';
@@ -8,18 +8,44 @@ import { now } from '../../../javascripts/modules/dates';
 
 
 describe('Timer', () => {
+  let wrapper;
   const mockedProps = {
     startTime: now(),
     endTime: null,
     isRunning: true,
-    state: 'warning',
+    status: 'warning',
   };
-  it('is valid', () => {
-    expect(React.isValidElement(<Timer {...mockedProps} />))
-    .to.equal(true);
+
+  beforeEach(() => {
+    wrapper = mount(<Timer {...mockedProps} />);
+  });
+
+  it('is a valid element', () => {
+    expect(React.isValidElement(<Timer {...mockedProps} />)).to.equal(true);
+  });
+
+  it('componentWillMount starts timer after 30ms and sets state.clockStr', () => {
+    expect(wrapper.state().clockStr).to.equal('');
+    setTimeout(() => {
+      expect(wrapper.state().clockStr).not.equal('');
+    }, 31);
   });
-  it('renders a span', () => {
-    const wrapper = shallow(<Timer {...mockedProps} />);
-    expect(wrapper.find('span')).to.have.length(1);
+
+  it('calls startTimer on mount', () => {
+    const startTimerSpy = sinon.spy(Timer.prototype, 'startTimer');
+    wrapper.mount();
+    expect(Timer.prototype.startTimer.calledOnce);
+    startTimerSpy.restore();
+  });
+
+  it('calls stopTimer on unmount', () => {
+    const stopTimerSpy = sinon.spy(Timer.prototype, 'stopTimer');
+    wrapper.unmount();
+    expect(Timer.prototype.stopTimer.calledOnce);
+    stopTimerSpy.restore();
+  });
+
+  it('renders a span with the correct class', () => {
+    expect(wrapper.find('span').hasClass('label-warning')).to.equal(true);
   });
 });