[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/util/dropOverflowsParent_spec.js

@@ -1,5 +1,3 @@
-import { expect } from 'chai';
-
 import dropOverflowsParent from '../../../../src/dashboard/util/dropOverflowsParent';
 import { NEW_COMPONENTS_SOURCE_ID } from '../../../../src/dashboard/util/constants';
 import {
@@ -40,7 +38,7 @@ describe('dropOverflowsParent', () => {
       },
     };
 
-    expect(dropOverflowsParent(dropResult, layout)).to.equal(true);
+    expect(dropOverflowsParent(dropResult, layout)).toBe(true);
   });
 
   it('returns false if a parent DOES have adequate width for child', () => {
@@ -72,7 +70,7 @@ describe('dropOverflowsParent', () => {
       },
     };
 
-    expect(dropOverflowsParent(dropResult, layout)).to.equal(false);
+    expect(dropOverflowsParent(dropResult, layout)).toBe(false);
   });
 
   it('returns false if a child CAN shrink to available parent space', () => {
@@ -104,7 +102,7 @@ describe('dropOverflowsParent', () => {
       },
     };
 
-    expect(dropOverflowsParent(dropResult, layout)).to.equal(false);
+    expect(dropOverflowsParent(dropResult, layout)).toBe(false);
   });
 
   it('returns true if a child CANNOT shrink to available parent space', () => {
@@ -137,7 +135,7 @@ describe('dropOverflowsParent', () => {
       },
     };
 
-    expect(dropOverflowsParent(dropResult, layout)).to.equal(true);
+    expect(dropOverflowsParent(dropResult, layout)).toBe(true);
   });
 
   it('returns true if a column has children that CANNOT shrink to available parent space', () => {
@@ -175,14 +173,14 @@ describe('dropOverflowsParent', () => {
       },
     };
 
-    expect(dropOverflowsParent(dropResult, layout)).to.equal(true);
+    expect(dropOverflowsParent(dropResult, layout)).toBe(true);
     // remove children
     expect(
       dropOverflowsParent(dropResult, {
         ...layout,
         dragging: { ...layout.dragging, children: [] },
       }),
-    ).to.equal(false);
+    ).toBe(false);
   });
 
   it('should work with new components that are not in the layout', () => {
@@ -200,7 +198,7 @@ describe('dropOverflowsParent', () => {
       },
     };
 
-    expect(dropOverflowsParent(dropResult, layout)).to.equal(false);
+    expect(dropOverflowsParent(dropResult, layout)).toBe(false);
   });
 
   it('source/destination without widths should not overflow parent', () => {
@@ -221,6 +219,6 @@ describe('dropOverflowsParent', () => {
       },
     };
 
-    expect(dropOverflowsParent(dropResult, layout)).to.equal(false);
+    expect(dropOverflowsParent(dropResult, layout)).toBe(false);
   });
 });