[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/modules/time_spec.js

@@ -1,5 +1,3 @@
-import { expect, assert } from 'chai';
-
 import moment from 'moment';
 import { getPlaySliderParams, truncate } from '../../../src/modules/time';
 
@@ -22,14 +20,14 @@ describe('truncate', () => {
     let result;
     isoDurations.forEach(([step, expected]) => {
       result = truncate(timestamp, step);
-      expect(result.format()).to.equal(expected.format());
+      expect(result.format()).toBe(expected.format());
     });
   });
 });
 
 describe('getPlaySliderParams', () => {
   it('is a function', () => {
-    assert.isFunction(getPlaySliderParams);
+    expect(typeof getPlaySliderParams).toBe('function');
   });
 
   it('handles durations', () => {
@@ -46,14 +44,14 @@ describe('getPlaySliderParams', () => {
       moment('2018-01-10T00:00:00'),
     ].map(d => parseInt(d.format('x'), 10));
     const { start, end, getStep, values, disabled } = getPlaySliderParams(timestamps, 'P2D');
-    expect(moment(start).format()).to.equal(moment('2018-01-01T00:00:00').format());
-    expect(moment(end).format()).to.equal(moment('2018-01-11T00:00:00').format());
-    expect(getStep(start)).to.equal(2 * 24 * 60 * 60 * 1000);
-    expect(values.map(v => moment(v).format())).to.eql([
+    expect(moment(start).format()).toBe(moment('2018-01-01T00:00:00').format());
+    expect(moment(end).format()).toBe(moment('2018-01-11T00:00:00').format());
+    expect(getStep(start)).toBe(2 * 24 * 60 * 60 * 1000);
+    expect(values.map(v => moment(v).format())).toEqual([
       moment('2018-01-01T00:00:00').format(),
       moment('2018-01-03T00:00:00').format(),
     ]);
-    expect(disabled).to.equal(false);
+    expect(disabled).toBe(false);
   });
 
   it('handles intervals', () => {
@@ -71,13 +69,13 @@ describe('getPlaySliderParams', () => {
     ].map(d => parseInt(d.format('x'), 10));
     // 1970-01-03 was a Saturday
     const { start, end, getStep, values, disabled } = getPlaySliderParams(timestamps, 'P1W/1970-01-03T00:00:00Z');
-    expect(moment(start).format()).to.equal(moment('2017-12-30T00:00:00Z').format());  // Saturday
-    expect(moment(end).format()).to.equal(moment('2018-01-13T00:00:00Z').format());  // Saturday
-    expect(getStep(start)).to.equal(7 * 24 * 60 * 60 * 1000);
-    expect(values.map(v => moment(v).format())).to.eql([
+    expect(moment(start).format()).toBe(moment('2017-12-30T00:00:00Z').format());  // Saturday
+    expect(moment(end).format()).toBe(moment('2018-01-13T00:00:00Z').format());  // Saturday
+    expect(getStep(start)).toBe(7 * 24 * 60 * 60 * 1000);
+    expect(values.map(v => moment(v).format())).toEqual([
       moment('2017-12-30T00:00:00Z').format(),
       moment('2018-01-06T00:00:00Z').format(),
     ]);
-    expect(disabled).to.equal(false);
+    expect(disabled).toBe(false);
   });
 });