diff --git a/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeTestBase.php b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeTestBase.php
index 23d5c295f3..c09b7ca723 100644
--- a/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeTestBase.php
+++ b/core/modules/migrate_drupal_ui/tests/src/Functional/MigrateUpgradeTestBase.php
@@ -97,28 +97,6 @@ protected function tearDown() {
     parent::tearDown();
   }
 
-  /**
-   * Transforms a nested array into a flat array suitable for BrowserTestBase::drupalPostForm().
-   *
-   * @param array $values
-   *   A multi-dimensional form values array to convert.
-   *
-   * @return array
-   *   The flattened $edit array suitable for BrowserTestBase::drupalPostForm().
-   */
-  protected function translatePostValues(array $values) {
-    $edit = [];
-    // The easiest and most straightforward way to translate values suitable for
-    // BrowserTestBase::drupalPostForm() is to actually build the POST data string
-    // and convert the resulting key/value pairs back into a flat array.
-    $query = http_build_query($values);
-    foreach (explode('&', $query) as $item) {
-      list($key, $value) = explode('=', $item);
-      $edit[urldecode($key)] = urldecode($value);
-    }
-    return $edit;
-  }
-
   /**
    * Tests the displayed upgrade paths.
    *
diff --git a/core/tests/Drupal/FunctionalTests/Installer/InstallerTestBase.php b/core/tests/Drupal/FunctionalTests/Installer/InstallerTestBase.php
index 55569a28d9..052b8b887f 100644
--- a/core/tests/Drupal/FunctionalTests/Installer/InstallerTestBase.php
+++ b/core/tests/Drupal/FunctionalTests/Installer/InstallerTestBase.php
@@ -262,28 +262,6 @@ protected function setUpSite() {
     $this->isInstalled = TRUE;
   }
 
-  /**
-   * Transforms a nested array into a flat array suitable for drupalPostForm().
-   *
-   * @param array $values
-   *   A multi-dimensional form values array to convert.
-   *
-   * @return array
-   *   The flattened $edit array suitable for BrowserTestBase::drupalPostForm().
-   */
-  protected function translatePostValues(array $values) {
-    $edit = [];
-    // The easiest and most straightforward way to translate values suitable for
-    // BrowserTestBase::drupalPostForm() is to actually build the POST data
-    // string and convert the resulting key/value pairs back into a flat array.
-    $query = http_build_query($values);
-    foreach (explode('&', $query) as $item) {
-      list($key, $value) = explode('=', $item);
-      $edit[urldecode($key)] = urldecode($value);
-    }
-    return $edit;
-  }
-
   /**
    * {@inheritdoc}
    *
diff --git a/core/tests/Drupal/Tests/BrowserTestBase.php b/core/tests/Drupal/Tests/BrowserTestBase.php
index c3c893ad2c..bc33a5c328 100644
--- a/core/tests/Drupal/Tests/BrowserTestBase.php
+++ b/core/tests/Drupal/Tests/BrowserTestBase.php
@@ -1316,6 +1316,28 @@ protected function getTestMethodCaller() {
     return $caller;
   }
 
+  /**
+   * Transforms a nested array into a flat array suitable for drupalPostForm().
+   *
+   * @param array $values
+   *   A multi-dimensional form values array to convert.
+   *
+   * @return array
+   *   The flattened $edit array suitable for BrowserTestBase::drupalPostForm().
+   */
+  protected function translatePostValues(array $values) {
+    $edit = [];
+    // The easiest and most straightforward way to translate values suitable for
+    // BrowserTestBase::drupalPostForm() is to actually build the POST data
+    // string and convert the resulting key/value pairs back into a flat array.
+    $query = http_build_query($values);
+    foreach (explode('&', $query) as $item) {
+      list($key, $value) = explode('=', $item);
+      $edit[urldecode($key)] = urldecode($value);
+    }
+    return $edit;
+  }
+
   /**
    * Checks for meta refresh tag and if found call drupalGet() recursively.
    *