improve expectRevert output

src/expectRevert.js

@@ -2,13 +2,19 @@ const { web3 } = require('./setup');
 
 const colors = require('ansi-colors');
 const semver = require('semver');
+const AssertionError = require('assert').AssertionError;
 
 async function expectException (promise, expectedError) {
   try {
     await promise;
   } catch (error) {
     if (error.message.indexOf(expectedError) === -1) {
-      throw Error(`Wrong failure type, expected '${expectedError}' and got '${error.message}'`);
+      const actualError = error.message.replace('Returned error: VM Exception while processing transaction: ', '');
+      throw new AssertionError({
+        message: 'Wrong failure type',
+        expected: expectedError,
+        actual: actualError,
+      });
     }
     return;
   }

test/helpers/assertFailure.js

@@ -1,9 +1,13 @@
 const { expect } = require('chai');
+const AssertionError = require('assert').AssertionError;
 
 async function assertFailure (promise) {
   try {
     await promise;
   } catch (error) {
+    if (error instanceof AssertionError) {
+      expect(error.message).to.equal('Wrong failure type');
+    }
     return;
   }
   expect.fail();