[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/DashboardBuilder_spec.jsx

@@ -1,7 +1,6 @@
 import { Provider } from 'react-redux';
 import React from 'react';
 import { shallow, mount } from 'enzyme';
-import { expect } from 'chai';
 
 import ParentSize from '@vx/responsive/build/components/ParentSize';
 import { Sticky, StickyContainer } from 'react-sticky';
@@ -47,21 +46,21 @@ describe('DashboardBuilder', () => {
   it('should render a StickyContainer with class "dashboard"', () => {
     const wrapper = setup();
     const stickyContainer = wrapper.find(StickyContainer);
-    expect(stickyContainer).to.have.length(1);
-    expect(stickyContainer.prop('className')).to.equal('dashboard');
+    expect(stickyContainer).toHaveLength(1);
+    expect(stickyContainer.prop('className')).toBe('dashboard');
   });
 
   it('should add the "dashboard--editing" class if editMode=true', () => {
     const wrapper = setup({ editMode: true });
     const stickyContainer = wrapper.find(StickyContainer);
-    expect(stickyContainer.prop('className')).to.equal(
+    expect(stickyContainer.prop('className')).toBe(
       'dashboard dashboard--editing',
     );
   });
 
   it('should render a DragDroppable DashboardHeader', () => {
     const wrapper = setup(null, true);
-    expect(wrapper.find(DashboardHeader)).to.have.length(1);
+    expect(wrapper.find(DashboardHeader)).toHaveLength(1);
   });
 
   it('should render a Sticky top-level Tabs if the dashboard has tabs', () => {
@@ -74,19 +73,19 @@ describe('DashboardBuilder', () => {
     const dashboardComponent = sticky.find(DashboardComponent);
 
     const tabChildren = layoutWithTabs.TABS_ID.children;
-    expect(sticky).to.have.length(1);
-    expect(dashboardComponent).to.have.length(1 + tabChildren.length); // tab + tabs
-    expect(dashboardComponent.at(0).prop('id')).to.equal('TABS_ID');
+    expect(sticky).toHaveLength(1);
+    expect(dashboardComponent).toHaveLength(1 + tabChildren.length); // tab + tabs
+    expect(dashboardComponent.at(0).prop('id')).toBe('TABS_ID');
     tabChildren.forEach((tabId, i) => {
-      expect(dashboardComponent.at(i + 1).prop('id')).to.equal(tabId);
+      expect(dashboardComponent.at(i + 1).prop('id')).toBe(tabId);
     });
   });
 
   it('should render a TabContainer and TabContent', () => {
     const wrapper = setup({ dashboardLayout: layoutWithTabs });
     const parentSize = wrapper.find(ParentSize).dive();
-    expect(parentSize.find(TabContainer)).to.have.length(1);
-    expect(parentSize.find(TabContent)).to.have.length(1);
+    expect(parentSize.find(TabContainer)).toHaveLength(1);
+    expect(parentSize.find(TabContent)).toHaveLength(1);
   });
 
   it('should set animation=true, mountOnEnter=true, and unmounOnExit=false on TabContainer for perf', () => {
@@ -96,9 +95,9 @@ describe('DashboardBuilder', () => {
       .dive()
       .find(TabContainer)
       .props();
-    expect(tabProps.animation).to.equal(true);
-    expect(tabProps.mountOnEnter).to.equal(true);
-    expect(tabProps.unmountOnExit).to.equal(false);
+    expect(tabProps.animation).toBe(true);
+    expect(tabProps.mountOnEnter).toBe(true);
+    expect(tabProps.unmountOnExit).toBe(false);
   });
 
   it('should render a TabPane and DashboardGrid for each Tab', () => {
@@ -106,16 +105,16 @@ describe('DashboardBuilder', () => {
     const parentSize = wrapper.find(ParentSize).dive();
 
     const expectedCount = layoutWithTabs.TABS_ID.children.length;
-    expect(parentSize.find(TabPane)).to.have.length(expectedCount);
-    expect(parentSize.find(DashboardGrid)).to.have.length(expectedCount);
+    expect(parentSize.find(TabPane)).toHaveLength(expectedCount);
+    expect(parentSize.find(DashboardGrid)).toHaveLength(expectedCount);
   });
 
   it('should render a BuilderComponentPane if editMode=showBuilderPane=true', () => {
     const wrapper = setup();
-    expect(wrapper.find(BuilderComponentPane)).to.have.length(0);
+    expect(wrapper.find(BuilderComponentPane)).toHaveLength(0);
 
     wrapper.setProps({ ...props, editMode: true, showBuilderPane: true });
-    expect(wrapper.find(BuilderComponentPane)).to.have.length(1);
+    expect(wrapper.find(BuilderComponentPane)).toHaveLength(1);
   });
 
   it('should change tabs if a top-level Tab is clicked', () => {
@@ -125,13 +124,13 @@ describe('DashboardBuilder', () => {
       mockStoreWithTabs,
     );
 
-    expect(wrapper.find(TabContainer).prop('activeKey')).to.equal(0);
+    expect(wrapper.find(TabContainer).prop('activeKey')).toBe(0);
 
     wrapper
       .find('.dashboard-component-tabs .nav-tabs a')
       .at(1)
       .simulate('click');
 
-    expect(wrapper.find(TabContainer).prop('activeKey')).to.equal(1);
+    expect(wrapper.find(TabContainer).prop('activeKey')).toBe(1);
   });
 });