consistent error handling in test callbacks

Like when an error is thrown, or a rejected promise is returned, if the error
is an Error instance use it as-is. Otherwise create an AssertionError.

Author: novemberborn

lib/test.js

@@ -197,11 +197,14 @@ Object.defineProperty(Test.prototype, 'end', {
 
 Test.prototype._end = function (err) {
 	if (err) {
-		this._setAssertError(new assert.AssertionError({
-			actual: err,
-			message: 'Callback called with an error → ' + err,
-			operator: 'callback'
-		}));
+		if (!(err instanceof Error)) {
+			err = new assert.AssertionError({
+				actual: err,
+				message: 'Callback called with an error: ' + inspect(err, {depth: null}),
+				operator: 'callback'
+			});
+		}
+		this._setAssertError(err);
 
 		this.exit();
 		return;

test/test.js

@@ -120,13 +120,26 @@ test('end can be used as callback without maintaining thisArg', function (t) {
 });
 
 test('end can be used as callback with error', function (t) {
+	var err = new Error('failed');
 	ava.cb(function (a) {
-		a.end(new Error('failed'));
+		a.end(err);
 	}).run().then(function (result) {
 		t.is(result.passed, false);
-		t.true(result.reason instanceof Error);
-		// TODO: Question - why not just set the reason to the error?
-		t.match(result.reason.message, /Callback called with an error/);
+		t.is(result.reason, err);
+		t.end();
+	});
+});
+
+test('end can be used as callback with a non-error as its error argument', function (t) {
+	var nonError = {foo: 'bar'};
+	ava.cb(function (a) {
+		a.end(nonError);
+	}).run().then(function (result) {
+		t.is(result.passed, false);
+		t.ok(result.reason);
+		t.is(result.reason.name, 'AssertionError');
+		t.is(result.reason.actual, nonError);
+		t.is(result.reason.message, 'Callback called with an error: { foo: \'bar\' }');
 		t.end();
 	});
 });