[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/OnPasteSelect_spec.jsx

@@ -1,7 +1,6 @@
 /* eslint-disable no-unused-expressions */
 import React from 'react';
 import sinon from 'sinon';
-import { expect } from 'chai';
 import { shallow } from 'enzyme';
 import VirtualizedSelect from 'react-virtualized-select';
 import Select, { Creatable } from 'react-select';
@@ -44,25 +43,25 @@ describe('OnPasteSelect', () => {
 
   it('renders the supplied selectWrap component', () => {
     const select = wrapper.find(Select);
-    expect(select).to.have.lengthOf(1);
+    expect(select).toHaveLength(1);
   });
 
   it('renders custom selectWrap components', () => {
     props.selectWrap = Creatable;
     wrapper = shallow(<OnPasteSelect {...props} />);
-    expect(wrapper.find(Creatable)).to.have.lengthOf(1);
+    expect(wrapper.find(Creatable)).toHaveLength(1);
     props.selectWrap = VirtualizedSelect;
     wrapper = shallow(<OnPasteSelect {...props} />);
-    expect(wrapper.find(VirtualizedSelect)).to.have.lengthOf(1);
+    expect(wrapper.find(VirtualizedSelect)).toHaveLength(1);
   });
 
   describe('onPaste', () => {
     it('calls onChange with pasted values', () => {
       wrapper.instance().onPaste(evt);
       expected = props.options.slice(0, 4);
-      expect(props.onChange.calledWith(expected)).to.be.true;
-      expect(evt.preventDefault.called).to.be.true;
-      expect(props.isValidNewOption.callCount).to.equal(5);
+      expect(props.onChange.calledWith(expected)).toBe(true);
+      expect(evt.preventDefault.called).toBe(true);
+      expect(props.isValidNewOption.callCount).toBe(5);
     });
 
     it('calls onChange without any duplicate values and adds new values', () => {
@@ -75,10 +74,10 @@ describe('OnPasteSelect', () => {
         { label: 'Chi na', value: 'Chi na' },
       ];
       wrapper.instance().onPaste(evt);
-      expect(props.onChange.calledWith(expected)).to.be.true;
-      expect(evt.preventDefault.called).to.be.true;
-      expect(props.isValidNewOption.callCount).to.equal(9);
-      expect(props.options[0].value).to.equal(expected[2].value);
+      expect(props.onChange.calledWith(expected)).toBe(true);
+      expect(evt.preventDefault.called).toBe(true);
+      expect(props.isValidNewOption.callCount).toBe(9);
+      expect(props.options[0].value).toBe(expected[2].value);
       props.options.splice(0, 1);
     });
 
@@ -96,9 +95,9 @@ describe('OnPasteSelect', () => {
         props.options[2],
       ];
       wrapper.instance().onPaste(evt);
-      expect(props.onChange.calledWith(expected)).to.be.true;
-      expect(evt.preventDefault.called).to.be.true;
-      expect(props.isValidNewOption.callCount).to.equal(11);
+      expect(props.onChange.calledWith(expected)).toBe(true);
+      expect(evt.preventDefault.called).toBe(true);
+      expect(props.isValidNewOption.callCount).toBe(11);
     });
   });
 });