[refactor] Migrate from Mocha+Chai to Jest (#6079)

* [refactor] Migrate from Mocha+Chai to Jest

This change migrates all the existing unit tests
- to Jest's global expect and matchers from chai's imported expect, asserts and matchers.
- to Jest's describe/test from mocha's describe/it

The majority of the mechanical changes to tests are achieved through running jest-codemods. The only two note-worthy manual tweaks:
1. Setting a testURL of http://localhost in jest config and adjusting a few tests to leverage this value instead of relying on about:blank.
2. Re-enabling ExploreChartPanel_spec which was previously commented out as we cannot have empty tests with nothing in it with Jest. :)

This change also removes dependencies to Mocha and Chai.

* Remove the test:one command as it now does the same thing as test.

* Fixing lint errors. The diff looks large but is large done through `yarn run lint --fix`

The only noteworthy change is the one in eslintrc for tests. The env has been updated from mocha to jest.

* Adding eslint-plugin-jest and further modify tests.

- One small fix in sqllab's Timer Spec for a test that is not using the spy it created for testing.
- Deletion of a duplicated test caught by eslint-plugin-jest.

* - Make istanbul coverage work with Jest.

- Remove dependency on stand-alone istanbul and babel-istanbul as they're built-into jest. Yes!

* Attempt to fix dynamic imports in tests.

* run sequentially and log heap usage

* - tweaking maxworkers for travis and specifying coverageDirectory for codecov

- remove dynamic import in shim.js now that it is set in babelrc for tests only.

superset/assets/spec/javascripts/components/AsyncSelect_spec.jsx

@@ -1,7 +1,6 @@
 import React from 'react';
 import Select from 'react-select';
 import { shallow } from 'enzyme';
-import { expect } from 'chai';
 import sinon from 'sinon';
 
 import AsyncSelect from '../../../src/components/AsyncSelect';
@@ -20,14 +19,14 @@ describe('AsyncSelect', () => {
   it('is valid element', () => {
     expect(
       React.isValidElement(<AsyncSelect {...mockedProps} />),
-    ).to.equal(true);
+    ).toBe(true);
   });
 
   it('has one select', () => {
     const wrapper = shallow(
       <AsyncSelect {...mockedProps} />,
     );
-    expect(wrapper.find(Select)).to.have.length(1);
+    expect(wrapper.find(Select)).toHaveLength(1);
   });
 
   it('calls onChange on select change', () => {
@@ -35,7 +34,7 @@ describe('AsyncSelect', () => {
       <AsyncSelect {...mockedProps} />,
     );
     wrapper.find(Select).simulate('change', { value: 1 });
-    expect(mockedProps.onChange).to.have.property('callCount', 1);
+    expect(mockedProps.onChange).toHaveProperty('callCount', 1);
   });
 
   describe('auto select', () => {
@@ -55,7 +54,7 @@ describe('AsyncSelect', () => {
       );
       wrapper.instance().fetchOptions();
       const spy = sinon.spy(wrapper.instance(), 'onChange');
-      expect(spy.callCount).to.equal(0);
+      expect(spy.callCount).toBe(0);
     });
     it('should auto select first option', () => {
       const wrapper = shallow(
@@ -64,8 +63,8 @@ describe('AsyncSelect', () => {
       const spy = sinon.spy(wrapper.instance(), 'onChange');
       server.respond();
 
-      expect(spy.callCount).to.equal(1);
-      expect(spy.calledWith(wrapper.instance().state.options[0])).to.equal(true);
+      expect(spy.callCount).toBe(1);
+      expect(spy.calledWith(wrapper.instance().state.options[0])).toBe(true);
     });
     it('should not auto select when value prop is set', () => {
       const wrapper = shallow(
@@ -75,8 +74,8 @@ describe('AsyncSelect', () => {
       wrapper.instance().fetchOptions();
       server.respond();
 
-      expect(spy.callCount).to.equal(0);
-      expect(wrapper.find(Select)).to.have.length(1);
+      expect(spy.callCount).toBe(0);
+      expect(wrapper.find(Select)).toHaveLength(1);
     });
   });
 });