Support use of t.end as callback, closes #180

* Binds all Test.prototype methods to current test.
* Checks for truthy error as first argument to Test.prototype.end.

lib/test.js

@@ -40,6 +40,10 @@ function Test(title, fn) {
 	if (this.title === 'callee$0$0') {
 		this.title = '[anonymous]';
 	}
+
+	Object.keys(Test.prototype).forEach(function (key) {
+		this[key] = this[key].bind(this);
+	}, this);
 }
 
 module.exports = Test;
@@ -147,7 +151,17 @@ Test.prototype.run = function () {
 	}.bind(this));
 };
 
-Test.prototype.end = function () {
+Test.prototype.end = function (err) {
+	if (err) {
+		this.assertError = new assert.AssertionError({
+			actual: err,
+			message: 'Callback called with an error → ' + err,
+			operator: 'callback'
+		});
+
+		return this.exit();
+	}
+
 	if (this.endCalled) {
 		throw new Error('.end() called more than once');
 	}

readme.md

@@ -339,6 +339,19 @@ test(async t => {
 
 *You don't have to manually call `t.end()`.*
 
+### Callback support
+
+AVA supports using `t.end` as the final callback when using node-style
+error-first callback APIs. AVA will consider any truthy value passed as
+the first argument to `t.end` to be an error.
+
+```js
+test(t => {
+	// t.end automatically checks for error as first argument
+	fs.readFile('data.txt', t.end);
+});
+```
+
 
 ## API
 

test/test.js

@@ -140,6 +140,24 @@ test('handle non-assertion errors', function (t) {
 	});
 });
 
+test('end can be used as callback without maintaining thisArg', function (t) {
+	ava(function (a) {
+		setTimeout(a.end);
+	}).run().then(function (a) {
+		t.false(a.assertError);
+		t.end();
+	});
+});
+
+test('end can be used as callback with error', function (t) {
+	ava(function (a) {
+		a.end(new Error('failed'));
+	}).run().catch(function (err) {
+		t.true(err instanceof Error);
+		t.end();
+	});
+});
+
 test('handle non-assertion errors even when planned', function (t) {
 	ava(function (a) {
 		a.plan(1);