improve expectRevert output

[dotrungkien]

fixes #33

• use AssertionError instead of plain Error as @frangio suggestion
• remove noisy Returned error: VM Exception while processing transaction: error substring from error.message

[frangio]

Nice @dotrungkien! Thanks!

Have you manually tested that this works? It would be good to have automated tests for this, which would also simplify testing it on different setups (like different ganache versions). We can open that as a different issue unless you're interested in tackling it as part of this pull request.

[dotrungkien]

@frangio thank you for your comment.
I've tested at local that everything is ok.
Can you write more details which test or setup should be added here ? I think different issue is not necessary.

[frangio]

@dotrungkien It would be a great step to add at least one test that the raised AssertionError has its message in the format that we want. So I think you should add one test in expectRevert.test.js that triggers an assertion error, kinda like this:

openzeppelin-test-helpers/test/src/expectRevert.test.js

Lines 40 to 42 in a4789e0

	it('rejects a failed requirement with incorrect expected reason', async function () {
	await assertFailure(expectRevert(this.reverter.revertFromRequireWithReason(), 'Wrong reason'));
	});

But instead of simply using assertFailure, catching that assertion error and checking that error.message has the right contents.

It might be a good idea to modify assertFailure to return the caught error.

openzeppelin-test-helpers/test/helpers/assertFailure.js

Lines 6 to 7 in a4789e0

	} catch (error) {
	return;

[dotrungkien]

@frangio
according to your comment, i've improved the implementation of AssertionError; and since we need to confirm the message is right or not, i've used throw AssertionError({message, expected, actual}) instead of assert.fail([message]) and then check the message in assertFailue.

thus, we not need to edit or add more test into expectRevert.test.js, because pass this case is just enough, i think:

openzeppelin-test-helpers/test/src/expectRevert.test.js

Lines 40 to 42 in a4789e0

	it('rejects a failed requirement with incorrect expected reason', async function () {
	await assertFailure(expectRevert(this.reverter.revertFromRequireWithReason(), 'Wrong reason'));
	});

all test passed with both ganache version above and bellow 2.2.0.

[frangio]

Implemented the missing parts myself. Thanks @dotrungkien!