[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/explore/components/SelectControl_spec.jsx

@@ -3,7 +3,6 @@ import React from 'react';
 import Select, { Creatable } from 'react-select';
 import VirtualizedSelect from 'react-virtualized-select';
 import sinon from 'sinon';
-import { expect } from 'chai';
 import { shallow } from 'enzyme';
 import OnPasteSelect from '../../../../src/components/OnPasteSelect';
 import VirtualizedRendererWrap from '../../../../src/components/VirtualizedRendererWrap';
@@ -29,43 +28,43 @@ describe('SelectControl', () => {
   });
 
   it('renders an OnPasteSelect', () => {
-    expect(wrapper.find(OnPasteSelect)).to.have.lengthOf(1);
+    expect(wrapper.find(OnPasteSelect)).toHaveLength(1);
   });
 
   it('calls onChange when toggled', () => {
     const select = wrapper.find(OnPasteSelect);
     select.simulate('change', { value: 50 });
-    expect(defaultProps.onChange.calledWith(50)).to.be.true;
+    expect(defaultProps.onChange.calledWith(50)).toBe(true);
   });
 
   it('passes VirtualizedSelect as selectWrap', () => {
     const select = wrapper.find(OnPasteSelect);
-    expect(select.props().selectWrap).to.equal(VirtualizedSelect);
+    expect(select.props().selectWrap).toBe(VirtualizedSelect);
   });
 
   it('passes Creatable as selectComponent when freeForm=true', () => {
     wrapper = shallow(<SelectControl {...defaultProps} freeForm />);
     const select = wrapper.find(OnPasteSelect);
-    expect(select.props().selectComponent).to.equal(Creatable);
+    expect(select.props().selectComponent).toBe(Creatable);
   });
 
   it('passes Select as selectComponent when freeForm=false', () => {
     const select = wrapper.find(OnPasteSelect);
-    expect(select.props().selectComponent).to.equal(Select);
+    expect(select.props().selectComponent).toBe(Select);
   });
 
   it('wraps optionRenderer in a VirtualizedRendererWrap', () => {
     const select = wrapper.find(OnPasteSelect);
     const defaultOptionRenderer = SelectControl.defaultProps.optionRenderer;
     const wrappedRenderer = VirtualizedRendererWrap(defaultOptionRenderer);
-    expect(select.props().optionRenderer).to.be.a('Function');
+    expect(typeof select.props().optionRenderer).toBe('function');
     // different instances of wrapper with same inner renderer are unequal
-    expect(select.props().optionRenderer.name).to.equal(wrappedRenderer.name);
+    expect(select.props().optionRenderer.name).toBe(wrappedRenderer.name);
   });
 
   describe('getOptions', () => {
     it('returns the correct options', () => {
-      expect(wrapper.instance().getOptions(defaultProps)).to.deep.equal(options);
+      expect(wrapper.instance().getOptions(defaultProps)).toEqual(options);
     });
 
     it('returns the correct options when freeform is set to true', () => {
@@ -78,7 +77,7 @@ describe('SelectControl', () => {
         { value: 'one', label: 'one' },
         { value: 'two', label: 'two' },
       ];
-      expect(wrapper.instance().getOptions(freeFormProps)).to.deep.equal(newOptions);
+      expect(wrapper.instance().getOptions(freeFormProps)).toEqual(newOptions);
     });
   });
 
@@ -95,7 +94,7 @@ describe('SelectControl', () => {
         value: null,
       };
       wrapper.setProps(newProps);
-      expect(wrapper.state().options).to.deep.equal(updatedOptions);
+      expect(wrapper.state().options).toEqual(updatedOptions);
     });
   });
 });