Allow parallel builds to be disabled

Fixes #2994.

Co-authored-by: Mark Wubben <mark@novemberborn.net>

docs/06-configuration.md

@@ -59,6 +59,7 @@ Arguments passed to the CLI will always take precedence over the CLI options con
 - `timeout`: Timeouts in AVA behave differently than in other test frameworks. AVA resets a timer after each test, forcing tests to quit if no new test results were received within the specified timeout. This can be used to handle stalled tests. See our [timeout documentation](./07-test-timeouts.md) for more options.
 - `nodeArguments`: Configure Node.js arguments used to launch worker processes.
 - `sortTestFiles`: A comparator function to sort test files with. Available only when using a `ava.config.*` file. See an example use case [here](recipes/splitting-tests-ci.md).
+- `utilizeParallelBuilds`: If `false`, disable [parallel builds](/docs/recipes/splitting-tests-ci.md) (default: true)
 
 Note that providing files on the CLI overrides the `files` option.
 

docs/recipes/splitting-tests-ci.md

@@ -2,6 +2,8 @@
 
 AVA automatically detects whether your CI environment supports parallel builds using [ci-parallel-vars](https://www.npmjs.com/package/ci-parallel-vars). When parallel builds support is detected, AVA sorts the all detected test files by name, and splits them into chunks. Each CI machine is assigned a chunk (subset) of the tests, and then each chunk is run in parallel.
 
+To disable this feature, set `utilizeParallelBuilds` to `false` in your [AVA configuration](/docs/06-configuration.md#options).
+
 To better distribute the tests across the machines, you can configure a custom comparator function:
 
 **`ava.config.js`:**
@@ -43,7 +45,7 @@ jobs:
     steps:
       # Check out code and perform setup steps
       # ...
-      
+
       - name: Test
         run: npx ava
         env:

lib/cli.js

@@ -393,7 +393,7 @@ export default async function loadCli() { // eslint-disable-line complexity
 	}
 
 	let parallelRuns = null;
-	if (isCi && ciParallelVars) {
+	if (isCi && ciParallelVars && combined.utilizeParallelBuilds !== false) {
 		const {index: currentIndex, total: totalRuns} = ciParallelVars;
 		parallelRuns = {currentIndex, totalRuns};
 	}