Exit with error if --watch is used in CI (#1203)

docs/recipes/watch-mode.md

@@ -83,6 +83,10 @@ Dependency tracking works for required modules. Custom extensions and transpiler
 
 The [`.only` modifier] disables watch mode's dependency tracking algorithm. When a change is made, all `.only` tests will be rerun, regardless of whether the test depends on the changed file.
 
+## Watch mode and CI
+
+If you run AVA in your CI with watch mode, the execution will exit with a error. AVA will not run with the `--watch` (`-w`) option in CI, because CI processes should terminate, and with the `--watch` option, AVA will never terminate.
+
 ## Manually rerunning all tests
 
 You can quickly rerun all tests by typing <kbd>r</kbd> on the console, followed by <kbd>Enter</kbd>.

lib/cli.js

@@ -99,6 +99,10 @@ exports.run = () => {
 		throw new Error(colors.error(figures.cross) + ' The TAP reporter is not available when using watch mode.');
 	}
 
+	if ((hasFlag('--watch') || hasFlag('-w')) && isCi) {
+		throw new Error(colors.error(figures.cross) + ' AVA will not run with the --watch (-w) option in CI, because CI processes should terminate, and with the --watch option, AVA will never terminate.');
+	}
+
 	if (hasFlag('--require') || hasFlag('-r')) {
 		throw new Error(colors.error(figures.cross) + ' The --require and -r flags are deprecated. Requirements should be configured in package.json - see documentation.');
 	}

test/cli.js

@@ -300,6 +300,16 @@ test('bails when config contains `"tap": true` and `"watch": true`', t => {
 	});
 });
 
+['--watch', '-w'].forEach(watchFlag => {
+	test(`bails when CI is used while ${watchFlag} is given`, t => {
+		execCli([watchFlag, 'test.js'], {dirname: 'fixture/watcher', env: {CI: true}}, (err, stdout, stderr) => {
+			t.is(err.code, 1);
+			t.match(stderr, 'AVA will not run with the --watch (-w) option in CI, because CI processes should terminate, and with the --watch option, AVA will never terminate.');
+			t.end();
+		});
+	});
+});
+
 test('--match works', t => {
 	execCli(['-m=foo', '-m=bar', '-m=!baz', '-m=t* a* f*', '-m=!t* a* n* f*', 'fixture/matcher-skip.js'], err => {
 		t.ifError(err);