[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/dashboard/components/dnd/DragDroppable_spec.jsx

@@ -1,6 +1,5 @@
 import React from 'react';
 import { shallow, mount } from 'enzyme';
-import { expect } from 'chai';
 import sinon from 'sinon';
 
 import newComponentFactory from '../../../../../src/dashboard/util/newComponentFactory';
@@ -33,18 +32,18 @@ describe('DragDroppable', () => {
 
   it('should render a div with class dragdroppable', () => {
     const wrapper = setup();
-    expect(wrapper.find('.dragdroppable')).to.have.length(1);
+    expect(wrapper.find('.dragdroppable')).toHaveLength(1);
   });
 
   it('should add class dragdroppable--dragging when dragging', () => {
     const wrapper = setup({ isDragging: true });
-    expect(wrapper.find('.dragdroppable')).to.have.length(1);
+    expect(wrapper.find('.dragdroppable')).toHaveLength(1);
   });
 
   it('should call its child function', () => {
     const childrenSpy = sinon.spy();
     setup({ children: childrenSpy });
-    expect(childrenSpy.callCount).to.equal(1);
+    expect(childrenSpy.callCount).toBe(1);
   });
 
   it('should call its child function with "dragSourceRef" if editMode=true', () => {
@@ -53,8 +52,8 @@ describe('DragDroppable', () => {
     setup({ children, editMode: false, dragSourceRef });
     setup({ children, editMode: true, dragSourceRef });
 
-    expect(children.getCall(0).args[0].dragSourceRef).to.equal(undefined);
-    expect(children.getCall(1).args[0].dragSourceRef).to.equal(dragSourceRef);
+    expect(children.getCall(0).args[0].dragSourceRef).toBeUndefined();
+    expect(children.getCall(1).args[0].dragSourceRef).toBe(dragSourceRef);
   });
 
   it('should call its child function with "dropIndicatorProps" dependent on editMode, isDraggingOver, state.dropIndicator is set', () => {
@@ -63,9 +62,9 @@ describe('DragDroppable', () => {
     wrapper.setState({ dropIndicator: 'nonsense' });
     wrapper.setProps({ ...props, editMode: true, isDraggingOver: true });
 
-    expect(children.callCount).to.equal(3); // initial + setState + setProps
-    expect(children.getCall(0).args[0].dropIndicatorProps).to.equal(undefined);
-    expect(children.getCall(2).args[0].dropIndicatorProps).to.deep.equal({
+    expect(children.callCount).toBe(3); // initial + setState + setProps
+    expect(children.getCall(0).args[0].dropIndicatorProps).toBeUndefined();
+    expect(children.getCall(2).args[0].dropIndicatorProps).toEqual({
       className: 'drop-indicator',
     });
   });
@@ -75,15 +74,15 @@ describe('DragDroppable', () => {
     const droppableRef = sinon.spy();
 
     setup({ dragPreviewRef, droppableRef }, true);
-    expect(dragPreviewRef.callCount).to.equal(1);
-    expect(droppableRef.callCount).to.equal(1);
+    expect(dragPreviewRef.callCount).toBe(1);
+    expect(droppableRef.callCount).toBe(1);
   });
 
   it('should set this.mounted dependent on life cycle', () => {
     const wrapper = setup({}, true);
     const instance = wrapper.instance();
-    expect(instance.mounted).to.equal(true);
+    expect(instance.mounted).toBe(true);
     wrapper.unmount();
-    expect(instance.mounted).to.equal(false);
+    expect(instance.mounted).toBe(false);
   });
 });