diff --git a/.github/workflows/reusable-phpunit-tests-v3.yml b/.github/workflows/reusable-phpunit-tests-v3.yml
index 6cae9a7530568..882ba5a715c86 100644
--- a/.github/workflows/reusable-phpunit-tests-v3.yml
+++ b/.github/workflows/reusable-phpunit-tests-v3.yml
@@ -247,6 +247,11 @@ jobs:
         with:
           custom-cache-suffix: $(/bin/date -u --date='last Mon' "+%F")
 
+      # Release branches run this workflow from trunk, but older branches lack this file.
+      - name: Select PHPUnit configuration
+        if: ${{ hashFiles('tests/phpunit/phpunit-config.php') != '' }}
+        run: echo "PHPUNIT_CONFIG=$(php ./tests/phpunit/phpunit-config.php "${PHPUNIT_CONFIG}")" >> "$GITHUB_ENV"
+
       - name: Install npm dependencies
         run: npm ci
 
@@ -293,20 +298,6 @@ jobs:
       - name: Install WordPress
         run: npm run env:install
 
-      - name: Select PHPUnit configuration
-        run: |
-          PHPUNIT_VERSION=$(node ./tools/local-env/scripts/docker.js run php ./vendor/bin/phpunit --version | grep -oE '\b[0-9]+\.[0-9]+' | head -n 1)
-          echo "Detected PHPUnit version: ${PHPUNIT_VERSION}"
-          MAJOR_VERSION=$(echo "${PHPUNIT_VERSION}" | cut -d. -f1)
-          if [ "${MAJOR_VERSION}" -ge 10 ]; then
-            if [ "${PHPUNIT_CONFIG}" = "tests/phpunit/multisite.xml" ]; then
-              NEW_CONFIG="tests/phpunit/multisite10.xml"
-            else
-              NEW_CONFIG="phpunit10.xml.dist"
-            fi
-            echo "Using PHPUnit 10+ configuration: ${NEW_CONFIG}"
-            echo "PHPUNIT_CONFIG=${NEW_CONFIG}" >> "$GITHUB_ENV"
-          fi
       - name: Run external HTTP tests
         if: ${{ ! inputs.multisite && ! inputs.phpunit-test-groups && ! inputs.coverage-report }}
         continue-on-error: ${{ inputs.allow-errors }}
diff --git a/.gitignore b/.gitignore
index 01c9060ac602d..74312255d037c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -10,7 +10,6 @@ wp-tests-config.php
 .phpunit.result.cache
 /phpunit.xml
 /phpunit10.xml
-/phpunit-10.xml
 /.phpcs.xml
 /phpcs.xml
 .cache/*
diff --git a/composer.json b/composer.json
index 1d08656534843..dcb058d3f5c21 100644
--- a/composer.json
+++ b/composer.json
@@ -81,7 +81,6 @@
 		"format": "@php ./vendor/squizlabs/php_codesniffer/bin/phpcbf --report=summary,source",
 		"lint": "@php ./vendor/squizlabs/php_codesniffer/bin/phpcs --report=summary,source",
 		"lint:errors": "@lint -n",
-		"test": [ "Composer\\Config::disableProcessTimeout", "@php ./vendor/phpunit/phpunit/phpunit" ],
-		"test10": [ "Composer\\Config::disableProcessTimeout", "@php ./vendor/phpunit/phpunit/phpunit -c phpunit10.xml.dist" ]
+		"test": [ "Composer\\Config::disableProcessTimeout", "@php ./vendor/phpunit/phpunit/phpunit -c \"$(php ./tests/phpunit/phpunit-config.php)\"" ]
 	}
 }
diff --git a/package.json b/package.json
index 215a8d3fd3a44..bf0d8340c435d 100644
--- a/package.json
+++ b/package.json
@@ -148,8 +148,7 @@
 		"env:logs": "node ./tools/local-env/scripts/docker.js logs",
 		"env:pull": "node ./tools/local-env/scripts/docker.js pull",
 		"test:performance": "wp-scripts test-playwright --config tests/performance/playwright.config.js",
-		"test:php": "node ./tools/local-env/scripts/docker.js run --rm php ./vendor/bin/phpunit",
-		"test:php10": "node ./tools/local-env/scripts/docker.js run --rm php ./vendor/bin/phpunit -c phpunit10.xml.dist",
+		"test:php": "node ./tools/local-env/scripts/docker.js run --rm php composer test --",
 		"test:coverage": "npm run test:php -- --coverage-html ./coverage/html/ --coverage-php ./coverage/php/report.php --coverage-text=./coverage/text/report.txt",
 		"test:e2e": "wp-scripts test-playwright --config tests/e2e/playwright.config.js",
 		"test:visual": "wp-scripts test-playwright --config tests/visual-regression/playwright.config.js",
diff --git a/tests/phpunit/README.md b/tests/phpunit/README.md
index 9500fe60f551e..01252d418f15a 100644
--- a/tests/phpunit/README.md
+++ b/tests/phpunit/README.md
@@ -8,20 +8,20 @@ For more information, please review the relevant Core Handbook pages:
 
 ## Configuration Files
 
-WordPress core maintains separate configuration files to support both PHPUnit 9 and PHPUnit 10.1+:
+WordPress core has separate configuration files for PHPUnit 9 and PHPUnit 10:
 
 - `phpunit.xml.dist` and `tests/phpunit/multisite.xml`: Used for PHPUnit 9 and earlier.
-- `phpunit10.xml.dist` and `tests/phpunit/multisite10.xml`: Used for PHPUnit 10.1 and later.
+- `phpunit10.xml.dist` and `tests/phpunit/multisite10.xml`: Used for PHPUnit 10 and later. These use the `<source>` element, so PHPUnit 10.0 is not supported.
 
 ### Running Tests Locally
 
-When running tests via Composer:
-- `composer test`: Runs tests using the default configuration (PHPUnit &lt; 10).
-- `composer test10`: Runs tests using `phpunit10.xml.dist` (PHPUnit 10+).
+`composer test` and `npm run test:php` use the single site configuration file that matches the installed version of PHPUnit. A local `phpunit.xml` file is used instead if one exists, so base it on the file that matches your version of PHPUnit.
 
-When running tests via npm and Docker:
-- `npm run test:php`: Runs tests using the default configuration.
-- `npm run test:php10`: Runs tests using `phpunit10.xml.dist`.
+`tests/phpunit/phpunit-config.php` prints the matching configuration file. Pass it either configuration file name to get the one for the installed version, for example to run the multisite tests:
+
+```
+./vendor/bin/phpunit -c "$(php tests/phpunit/phpunit-config.php tests/phpunit/multisite.xml)"
+```
 
 ## Run the full matrix on a pull request
 
diff --git a/tests/phpunit/phpunit-config.php b/tests/phpunit/phpunit-config.php
new file mode 100644
index 0000000000000..3b2a16ee970a8
--- /dev/null
+++ b/tests/phpunit/phpunit-config.php
@@ -0,0 +1,51 @@
+<?php
+/**
+ * Prints the PHPUnit configuration file that matches the installed version of PHPUnit.
+ *
+ * PHPUnit 10 changed the configuration file format, so PHPUnit 9 and earlier use
+ * phpunit.xml.dist and tests/phpunit/multisite.xml, while PHPUnit 10 and later use
+ * phpunit10.xml.dist and tests/phpunit/multisite10.xml.
+ *
+ * Pass one of those files to get its counterpart for the installed version. Any other file
+ * is printed unchanged. With no argument, a local phpunit.xml is printed if one exists,
+ * otherwise the single site configuration file for the installed version.
+ *
+ * The printed path is relative to the root of the repository.
+ *
+ * Usage: ./vendor/bin/phpunit -c "$(php tests/phpunit/phpunit-config.php [file])"
+ */
+
+$root = dirname( __DIR__, 2 );
+
+$installed     = require $root . '/vendor/composer/installed.php';
+$is_phpunit_10 = version_compare( $installed['versions']['phpunit/phpunit']['version'], '10', '>=' );
+
+$swaps = array(
+	'phpunit.xml.dist'            => 'phpunit10.xml.dist',
+	'tests/phpunit/multisite.xml' => 'tests/phpunit/multisite10.xml',
+);
+
+if ( ! $is_phpunit_10 ) {
+	$swaps = array_flip( $swaps );
+}
+
+if ( ! isset( $argv[1] ) ) {
+	if ( file_exists( $root . '/phpunit.xml' ) ) {
+		echo 'phpunit.xml';
+	} else {
+		echo $is_phpunit_10 ? 'phpunit10.xml.dist' : 'phpunit.xml.dist';
+	}
+	exit;
+}
+
+$config = $argv[1];
+$real   = realpath( $config );
+
+foreach ( $swaps as $from => $to ) {
+	if ( false !== $real && realpath( $root . '/' . $from ) === $real ) {
+		$config = $to;
+		break;
+	}
+}
+
+echo $config;