Make the Promise interface complete by adding a .finally() method (#…

…174)

Fixes #147

index.js

@@ -316,6 +316,10 @@ module.exports = (command, args, options) => {
 
 	spawned.then = (onfulfilled, onrejected) => handlePromise().then(onfulfilled, onrejected);
 	spawned.catch = onrejected => handlePromise().catch(onrejected);
+	// eslint-disable-next-line no-use-extend-native/no-use-extend-native
+	if (Promise.prototype.finally) {
+		spawned.finally = onfinally => handlePromise().finally(onfinally);
+	}
 
 	return spawned;
 };

test.js

@@ -519,3 +519,39 @@ test('removes exit handler on exit', async t => {
 	const included = ee.listeners('exit').includes(listener);
 	t.false(included);
 });
+
+// eslint-disable-next-line no-use-extend-native/no-use-extend-native
+if (Promise.prototype.finally) {
+	test('finally function is executed on success', async t => {
+		let called = false;
+		const {stdout} = await m('noop', ['foo']).finally(() => {
+			called = true;
+		});
+		t.is(called, true);
+		t.is(stdout, 'foo');
+	});
+
+	test('finally function is executed on failure', async t => {
+		let called = false;
+		const err = await t.throws(m('exit', ['2']).finally(() => {
+			called = true;
+		}));
+		t.is(called, true);
+		t.is(typeof err.stdout, 'string');
+		t.is(typeof err.stderr, 'string');
+	});
+
+	test('throw in finally function bubbles up on success', async t => {
+		const result = await t.throws(m('noop', ['foo']).finally(() => {
+			throw new Error('called');
+		}));
+		t.is(result.message, 'called');
+	});
+
+	test('throw in finally bubbles up on error', async t => {
+		const result = await t.throws(m('exit', ['2']).finally(() => {
+			throw new Error('called');
+		}));
+		t.is(result.message, 'called');
+	});
+}