diff --git a/src/DrupalCI/Plugin/BuildTask/BuildStep/Testing/Simpletest.php b/src/DrupalCI/Plugin/BuildTask/BuildStep/Testing/Simpletest.php
index e3c30252..2fb0e641 100644
--- a/src/DrupalCI/Plugin/BuildTask/BuildStep/Testing/Simpletest.php
+++ b/src/DrupalCI/Plugin/BuildTask/BuildStep/Testing/Simpletest.php
@@ -141,9 +141,10 @@ class Simpletest extends BuildTaskBase implements BuildStepInterface, BuildTaskI
 
     $command = ["cd " . $this->environment->getExecContainerSourceDir() . " && sudo -u www-data php " . $this->environment->getExecContainerSourceDir() . $this->runscript];
 
-    if ($is_extension_test) {
-      // Always add --suppress-deprecations for contrib. getRunTestsFlagValues()
-      // will determine whether to add it based on core version.
+    if ($is_extension_test && $this->configuration['suppress-deprecations'] === NULL ) {
+      // Always add --suppress-deprecations for contrib if there is no
+      // environment variable set. getRunTestsFlagValues() will determine
+      // whether to add it based on core version.
       // @todo Turn this off when some other solution is decided in
       //   https://www.drupal.org/project/drupal/issues/2607260
       $this->configuration['suppress-deprecations'] = TRUE;
@@ -204,7 +205,8 @@ class Simpletest extends BuildTaskBase implements BuildStepInterface, BuildTaskI
       // testing modules or themes?
       'extension_test' => FALSE,
       'core_branch' => '8.4.x',
-      'suppress-deprecations' => FALSE,
+      // NULL means that this has not been configured.
+      'suppress-deprecations' => NULL,
     ];
   }
 
diff --git a/tests/DrupalCI/Tests/Plugin/BuildTask/BuildStep/Testing/SimpletestTest.php b/tests/DrupalCI/Tests/Plugin/BuildTask/BuildStep/Testing/SimpletestTest.php
index 37a081a9..74634a26 100644
--- a/tests/DrupalCI/Tests/Plugin/BuildTask/BuildStep/Testing/SimpletestTest.php
+++ b/tests/DrupalCI/Tests/Plugin/BuildTask/BuildStep/Testing/SimpletestTest.php
@@ -17,7 +17,15 @@ class SimpletestTest extends DrupalCITestCase {
     return [
       'core' => [
         'cd exec-container-source-dir && sudo -u www-data php exec-container-source-dir/core/scripts/run-tests.sh --color --keep-results --values=value --all',
-        [],
+        ['core_branch' => '8.5.x'],
+      ],
+      'core-8.5.x-suppress-deprecations' => [
+        'cd exec-container-source-dir && sudo -u www-data php exec-container-source-dir/core/scripts/run-tests.sh --color --keep-results --suppress-deprecations --values=value --all',
+        ['core_branch' => '8.5.x', 'suppress-deprecations' => TRUE],
+      ],
+      'core-8.4.x-suppress-deprecations-flag' => [
+        'cd exec-container-source-dir && sudo -u www-data php exec-container-source-dir/core/scripts/run-tests.sh --color --keep-results --values=value --all',
+        ['core_branch' => '8.4.x', 'suppress-deprecations' => TRUE],
       ],
       'contrib-default' => [
         'cd exec-container-source-dir && sudo -u www-data php exec-container-source-dir/core/scripts/run-tests.sh --color --keep-results --values=value --directory true-extension-subdirectory',
@@ -27,10 +35,22 @@ class SimpletestTest extends DrupalCITestCase {
         'cd exec-container-source-dir && sudo -u www-data php exec-container-source-dir/core/scripts/run-tests.sh --color --keep-results --values=value --directory true-extension-subdirectory',
         ['extension_test' => TRUE, 'core_branch' => '8.4.x'],
       ],
+      'contrib-8.4.x-suppress-deprecations-true' => [
+        'cd exec-container-source-dir && sudo -u www-data php exec-container-source-dir/core/scripts/run-tests.sh --color --keep-results --values=value --directory true-extension-subdirectory',
+        ['extension_test' => TRUE, 'core_branch' => '8.4.x', 'suppress-deprecations' => TRUE],
+      ],
       'contrib-8.5.x' => [
         'cd exec-container-source-dir && sudo -u www-data php exec-container-source-dir/core/scripts/run-tests.sh --color --keep-results --suppress-deprecations --values=value --directory true-extension-subdirectory',
         ['extension_test' => TRUE, 'core_branch' => '8.5.x'],
       ],
+      'contrib-8.5.x-suppress-deprecations-false' => [
+        'cd exec-container-source-dir && sudo -u www-data php exec-container-source-dir/core/scripts/run-tests.sh --color --keep-results --values=value --directory true-extension-subdirectory',
+        ['extension_test' => TRUE, 'core_branch' => '8.5.x', 'suppress-deprecations' => FALSE],
+      ],
+      'contrib-8.5.x-suppress-deprecations-true' => [
+        'cd exec-container-source-dir && sudo -u www-data php exec-container-source-dir/core/scripts/run-tests.sh --color --keep-results --suppress-deprecations --values=value --directory true-extension-subdirectory',
+        ['extension_test' => TRUE, 'core_branch' => '8.5.x', 'suppress-deprecations' => TRUE],
+      ],
     ];
   }