[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/dates_spec.js

@@ -1,4 +1,3 @@
-import { assert, expect } from 'chai';
 import {
   tickMultiFormat,
   formatDate,
@@ -12,102 +11,102 @@ import {
 
 describe('tickMultiFormat', () => {
   it('is a function', () => {
-    assert.isFunction(tickMultiFormat);
+    expect(typeof tickMultiFormat).toBe('function');
   });
 });
 
 describe('formatDate', () => {
   it('is a function', () => {
-    assert.isFunction(formatDate);
+    expect(typeof formatDate).toBe('function');
   });
 
   it('shows only year when 1st day of the year', () => {
-    expect(formatDate(new Date('2020-01-01'))).to.equal('2020');
+    expect(formatDate(new Date('2020-01-01'))).toBe('2020');
   });
 
   it('shows only month when 1st of month', () => {
-    expect(formatDate(new Date('2020-03-01'))).to.equal('March');
+    expect(formatDate(new Date('2020-03-01'))).toBe('March');
   });
 
   it('does not show day of week when it is Sunday', () => {
-    expect(formatDate(new Date('2020-03-15'))).to.equal('Mar 15');
+    expect(formatDate(new Date('2020-03-15'))).toBe('Mar 15');
   });
 
   it('shows weekday when it is not Sunday (and no ms/sec/min/hr)', () => {
-    expect(formatDate(new Date('2020-03-03'))).to.equal('Tue 03');
+    expect(formatDate(new Date('2020-03-03'))).toBe('Tue 03');
   });
 });
 
 describe('formatDateVerbose', () => {
   it('is a function', () => {
-    assert.isFunction(formatDateVerbose);
+    expect(typeof formatDateVerbose).toBe('function');
   });
 
   it('shows only year when 1st day of the year', () => {
-    expect(formatDateVerbose(new Date('2020-01-01'))).to.equal('2020');
+    expect(formatDateVerbose(new Date('2020-01-01'))).toBe('2020');
   });
 
   it('shows month and year when 1st of month', () => {
-    expect(formatDateVerbose(new Date('2020-03-01'))).to.equal('Mar 2020');
+    expect(formatDateVerbose(new Date('2020-03-01'))).toBe('Mar 2020');
   });
 
   it('shows weekday when any day of the month', () => {
-    expect(formatDateVerbose(new Date('2020-03-03'))).to.equal('Tue Mar 3');
-    expect(formatDateVerbose(new Date('2020-03-15'))).to.equal('Sun Mar 15');
+    expect(formatDateVerbose(new Date('2020-03-03'))).toBe('Tue Mar 3');
+    expect(formatDateVerbose(new Date('2020-03-15'))).toBe('Sun Mar 15');
   });
 });
 
 describe('fDuration', () => {
   it('is a function', () => {
-    assert.isFunction(fDuration);
+    expect(typeof fDuration).toBe('function');
   });
 
   it('returns a string', () => {
-    expect(fDuration(new Date(), new Date())).to.be.a('string');
+    expect(typeof fDuration(new Date(), new Date())).toBe('string');
   });
 
   it('returns the expected output', () => {
     const output = fDuration('1496293608897', '1496293623406');
-    expect(output).to.equal('00:00:14.50');
+    expect(output).toBe('00:00:14.50');
   });
 });
 
 describe('now', () => {
   it('is a function', () => {
-    assert.isFunction(now);
+    expect(typeof now).toBe('function');
   });
 
   it('returns a number', () => {
-    expect(now()).to.be.a('number');
+    expect(typeof now()).toBe('number');
   });
 });
 
 describe('epochTimeXHoursAgo', () => {
   it('is a function', () => {
-    assert.isFunction(epochTimeXHoursAgo);
+    expect(typeof epochTimeXHoursAgo).toBe('function');
   });
 
   it('returns a number', () => {
-    expect(epochTimeXHoursAgo(1)).to.be.a('number');
+    expect(typeof epochTimeXHoursAgo(1)).toBe('number');
   });
 });
 
 describe('epochTimeXDaysAgo', () => {
   it('is a function', () => {
-    assert.isFunction(epochTimeXDaysAgo);
+    expect(typeof epochTimeXDaysAgo).toBe('function');
   });
 
   it('returns a number', () => {
-    expect(epochTimeXDaysAgo(1)).to.be.a('number');
+    expect(typeof epochTimeXDaysAgo(1)).toBe('number');
   });
 });
 
 describe('epochTimeXYearsAgo', () => {
   it('is a function', () => {
-    assert.isFunction(epochTimeXYearsAgo);
+    expect(typeof epochTimeXYearsAgo).toBe('function');
   });
 
   it('returns a number', () => {
-    expect(epochTimeXYearsAgo(1)).to.be.a('number');
+    expect(typeof epochTimeXYearsAgo(1)).toBe('number');
   });
 });