[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/addSlice/AddSliceContainer_spec.jsx

@@ -1,5 +1,4 @@
 import React from 'react';
-import { expect } from 'chai';
 import { shallow } from 'enzyme';
 import { Button } from 'react-bootstrap';
 import Select from 'react-virtualized-select';
@@ -20,19 +19,19 @@ describe('AddSliceContainer', () => {
   });
 
   it('uses table as default visType', () => {
-    expect(wrapper.state().visType).to.equal('table');
+    expect(wrapper.state().visType).toBe('table');
   });
 
   it('renders 2 selects', () => {
-    expect(wrapper.find(Select)).to.have.lengthOf(2);
+    expect(wrapper.find(Select)).toHaveLength(2);
   });
 
   it('renders a button', () => {
-    expect(wrapper.find(Button)).to.have.lengthOf(1);
+    expect(wrapper.find(Button)).toHaveLength(1);
   });
 
   it('renders a disabled button if no datasource is selected', () => {
-    expect(wrapper.find(Button).dive().find('.btn[disabled=true]')).to.have.length(1);
+    expect(wrapper.find(Button).dive().find('.btn[disabled=true]')).toHaveLength(1);
   });
 
   it('renders an enabled button if datasource is selected', () => {
@@ -42,7 +41,7 @@ describe('AddSliceContainer', () => {
       datasourceId: datasourceValue.split('__')[0],
       datasourceType: datasourceValue.split('__')[1],
     });
-    expect(wrapper.find(Button).dive().find('.btn[disabled=false]')).to.have.length(1);
+    expect(wrapper.find(Button).dive().find('.btn[disabled=false]')).toHaveLength(1);
   });
 
   it('formats explore url', () => {
@@ -53,6 +52,6 @@ describe('AddSliceContainer', () => {
       datasourceType: datasourceValue.split('__')[1],
     });
     const formattedUrl = '/superset/explore/?form_data=%7B%22viz_type%22%3A%22table%22%2C%22datasource%22%3A%221__table%22%7D';
-    expect(wrapper.instance().exploreUrl()).to.equal(formattedUrl);
+    expect(wrapper.instance().exploreUrl()).toBe(formattedUrl);
   });
 });