PHPLIB-688 Report serverless mode in unified test runner

Author: alcaeus

CONTRIBUTING.md

@@ -34,7 +34,8 @@ The `phpunit.xml.dist` file is used as the default configuration file for the
 test suite. In addition to various PHPUnit options, it defines required
 `MONGODB_URI` and `MONGODB_DATABASE` environment variables. You may customize
 this configuration by creating your own `phpunit.xml` file based on the
-`phpunit.xml.dist` file we provide.
+`phpunit.xml.dist` file we provide. To run the tests in serverless mode, set the
+`MONGODB_IS_SERVERLESS` environment variable to `on`.
 
 By default, the `simple-phpunit` binary chooses the correct PHPUnit version for
 the PHP version you are running. To run tests against a specific PHPUnit version,

tests/UnifiedSpecTests/UnifiedTestRunner.php

@@ -19,7 +19,9 @@
 
 use function call_user_func;
 use function count;
+use function filter_var;
 use function gc_collect_cycles;
+use function getenv;
 use function in_array;
 use function is_string;
 use function PHPUnit\Framework\assertContainsOnly;
@@ -33,6 +35,8 @@
 use function strpos;
 use function version_compare;
 
+use const FILTER_VALIDATE_BOOLEAN;
+
 /**
  * Unified test runner.
  *
@@ -339,8 +343,9 @@ private function isAuthenticated(): bool
      */
     private function isServerless(): bool
     {
-        // TODO: detect serverless once PHPC-1755 is implemented
-        return false;
+        $isServerless = getenv('MONGODB_IS_SERVERLESS');
+
+        return $isServerless !== false ? filter_var($isServerless, FILTER_VALIDATE_BOOLEAN) : false;
     }
 
     /**