refactoring test/

pull test cases to `common-testCases.js` and `common-testCases-error.js`
framework tests then includes these files to reduces duplication and make tests more consistent between the frameworks

 On branch test-refactor
 Changes to be committed:
	new file:   test/common-testCases-error.js
	new file:   test/common-testCases.js
	modified:   test/core-handleError.js
	modified:   test/core.js
	modified:   test/express-handleError.js
	modified:   test/express.js
	modified:   test/union-handleError.js
	modified:   test/union.js
[test] Simplify exports and variable names