Fail hard when --concurrency is used without a value (#1373)

Author: yatharthx

lib/cli.js

@@ -118,6 +118,10 @@ exports.run = () => {
 		throw new Error(colors.error(figures.cross) + ' Watch mode is not available in CI, as it prevents AVA from terminating.');
 	}
 
+	if (cli.flags.concurrency === '') {
+		throw new Error(colors.error(figures.cross) + ' The --concurrency and -c flags must be provided the maximum number of test files to run at once.');
+	}
+
 	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

@@ -364,6 +364,25 @@ test('bails when config contains `"tap": true` and `"watch": true`', t => {
 	});
 });
 
+['--concurrency', '-c'].forEach(concurrencyFlag => {
+	test(`bails when ${concurrencyFlag} provided without value`, t => {
+		execCli(['test.js', concurrencyFlag], {dirname: 'fixture/concurrency'}, (err, stdout, stderr) => {
+			t.is(err.code, 1);
+			t.match(stderr, 'The --concurrency and -c flags must be provided the maximum number of test files to run at once.');
+			t.end();
+		});
+	});
+});
+
+['--concurrency', '-c'].forEach(concurrencyFlag => {
+	test(`works when ${concurrencyFlag} provided with value`, t => {
+		execCli([`${concurrencyFlag}=1`, 'test.js'], {dirname: 'fixture/concurrency'}, err => {
+			t.ifError(err);
+			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);

test/fixture/concurrency/test.js

@@ -0,0 +1,5 @@
+import test from '../../../';
+
+test('works', t => {
+	t.pass();
+});