test_runner: introduces test_concurrency flag

adds the test_concurrency flag,
if set to true, runs all the tests in parallel

Fixes: nodejs#43837

doc/api/cli.md

@@ -1116,6 +1116,14 @@ Starts the Node.js command line test runner. This flag cannot be combined with
 `--check`, `--eval`, `--interactive`, or the inspector. See the documentation
 on [running tests from the command line][] for more details.
 
+### `--test-concurrency`
+
+<!-- YAML
+added: REPLACEME
+-->
+
+Configures the test runner to run sub tests in parallel.
+
 ### `--test-only`
 
 <!-- YAML

lib/internal/test_runner/test.js

@@ -48,7 +48,6 @@ const isTestRunner = getOptionValue('--test');
 const testOnlyFlag = !isTestRunner && getOptionValue('--test-only');
 // TODO(cjihrig): Use uv_available_parallelism() once it lands.
 const rootConcurrency = isTestRunner ? cpus().length : 1;
-
 const kShouldAbort = Symbol('kShouldAbort');
 
 

src/node_options.cc

@@ -529,6 +529,9 @@ EnvironmentOptionsParser::EnvironmentOptionsParser() {
   AddOption("--test",
             "launch test runner on startup",
             &EnvironmentOptions::test_runner);
+  AddOption("--test-concurrency",
+            "tests defined within a file run in parallel",
+            &EnvironmentOptions::test_concurrency);
   AddOption("--test-only",
             "run tests with 'only' option set",
             &EnvironmentOptions::test_only,

src/node_options.h

@@ -151,6 +151,7 @@ class EnvironmentOptions : public Options {
   std::string redirect_warnings;
   std::string diagnostic_dir;
   bool test_runner = false;
+  bool test_concurrency = false;
   bool test_only = false;
   bool test_udp_no_try_send = false;
   bool throw_deprecation = false;