Add the test-title-format rule

Fix avajs#157

Author: GMartigny

docs/rules/test-title-format.md

@@ -0,0 +1,59 @@
+# Ensure tests have a correct title format
+
+Translations: 
+
+Tests should have a title matching the format option.
+
+
+## Fail
+
+```js
+/*eslint ava/test-title: ["error", {regexp: "^Should"}]*/
+import test from 'ava';
+
+test("Not starting with 'Should'", t => {
+	t.pass();
+});
+
+/*eslint ava/test-title: ["error", {regexp: "\\.$"}]*/
+import test from 'ava';
+
+test('Doesn\'t end with a dot', t => {
+	t.pass();
+});
+```
+
+
+## Pass
+
+```js
+/*eslint ava/test-title: ["error", {regexp: "^Should"}]*/
+import test from 'ava';
+
+test('Should pass tests', t => {
+	t.pass();
+});
+
+test('Should behave as expected', t => {
+	t.pass();
+});
+
+/*eslint ava/test-title: ["error", {regexp: "\\.$"}]*/
+import test from 'ava';
+
+test('End with a dot.', t => {
+	t.pass();
+});
+```
+
+## Options
+
+This rule supports the following options:
+
+`regexp`: A regular expression string to match against the test titles. Overrides the default and the configuration found in the `package.json` or `ava.config.js` files.
+
+You can set the options like this:
+
+```js
+"ava/test-title-format": ["error", {"regexp": "^Should"}]
+```

rules/test-title-format.js

@@ -0,0 +1,46 @@
+'use strict';
+const {visitIf} = require('enhance-visitors');
+const createAvaRule = require('../create-ava-rule');
+const util = require('../util');
+
+const create = context => {
+	const ava = createAvaRule();
+	let titleRegExp;
+	try {
+		if (context.options[0] && context.options[0].regexp) {
+			titleRegExp = new RegExp(context.options[0].regexp);
+		}
+	} catch (error) {
+		console.warn(error);
+	}
+
+	return ava.merge({
+		CallExpression: visitIf([
+			ava.isInTestFile,
+			ava.isTestNode,
+			ava.hasNoHookModifier
+		])(node => {
+			const requiredLength = ava.hasTestModifier('todo') ? 1 : 2;
+			const hasTitle = node.arguments.length >= requiredLength;
+
+			if (hasTitle && titleRegExp) {
+				const title = node.arguments[0];
+				if (title.type === 'Literal' && !titleRegExp.test(title.value)) {
+					context.report({
+						node,
+						message: 'Title doesn\'t match required format.'
+					});
+				}
+			}
+		})
+	});
+};
+
+module.exports = {
+	create,
+	meta: {
+		docs: {
+			url: util.getDocsUrl(__filename)
+		}
+	}
+};

test/test-title-format.js

@@ -0,0 +1,63 @@
+import test from 'ava';
+import avaRuleTester from 'eslint-ava-rule-tester';
+import rule from '../rules/test-title-format';
+
+const ruleTester = avaRuleTester(test, {
+	env: {
+		es6: true
+	}
+});
+
+const errors = [{ruleId: 'test-title-format'}];
+const header = 'const test = require(\'ava\');\n';
+
+ruleTester.run('test-title-format', rule, {
+	valid: [
+		header + 'test("Foo", t => { t.pass(); });',
+		{
+			code: header + 'test("Foo", t => { t.pass(); });',
+			options: [{regexp: '.'}]
+		},
+		{
+			code: header + 'test("Should pass tests.", t => { t.pass(); });',
+			options: [{regexp: '^Should .+\\.$'}]
+		},
+		{
+			code: header + 'test.todo("Should pass tests.");',
+			options: [{regexp: '^Should .+\\.$'}]
+		},
+		{
+			code: header + 'test(t => { t.pass(); });',
+			options: [{regexp: '^Should'}]
+		},
+		{
+			code: header + 'test("Foo", t => { t.pass(); });',
+			options: [{regexp: '(]'}] // Invalid regexp
+		},
+		{
+			code: header + 'notTest("Foo", t => { t.pass(); });',
+			options: [{regexp: '^Should'}]
+		},
+		{
+			code: header + 'test(macro, t => { t.pass(); });',
+			options: [{regexp: '^Should'}]
+		},
+		// Shouldn't be triggered since it's not a test file
+		{
+			code: 'test("Test", t => { t.pass(); });',
+			options: [{regexp: '^Should'}]
+		}
+	],
+	invalid: [
+		{
+			code: header + 'test("Test something", t => { t.pass(); });',
+			options: [{regexp: '^Should'}],
+			errors
+		},
+		{
+			code: header + 'test.todo("Test something");',
+			options: [{regexp: '^Should'}],
+			errors
+		},
+	]
+});