diff --git a/tests/Composer/Test/ConfigTest.php b/tests/Composer/Test/ConfigTest.php
index 69a64397b4c9..9fe1da3fcf22 100644
--- a/tests/Composer/Test/ConfigTest.php
+++ b/tests/Composer/Test/ConfigTest.php
@@ -409,7 +409,7 @@ public function testGetDefaultsToAnEmptyArray(): void
         }
     }
 
-    public function testMergesPluginConfig()
+    public function testMergesPluginConfig(): void
     {
         $config = new Config(false);
         $config->merge(array('config' => array('allow-plugins' => array('some/plugin' => true))));
@@ -419,7 +419,7 @@ public function testMergesPluginConfig()
         $this->assertEquals(array('some/plugin' => true, 'another/plugin' => true), $config->get('allow-plugins'));
     }
 
-    public function testOverridesGlobalBooleanPluginsConfig()
+    public function testOverridesGlobalBooleanPluginsConfig(): void
     {
         $config = new Config(false);
         $config->merge(array('config' => array('allow-plugins' => true)));
@@ -429,7 +429,7 @@ public function testOverridesGlobalBooleanPluginsConfig()
         $this->assertEquals(array('another/plugin' => true), $config->get('allow-plugins'));
     }
 
-    public function testAllowsAllPluginsFromLocalBoolean()
+    public function testAllowsAllPluginsFromLocalBoolean(): void
     {
         $config = new Config(false);
         $config->merge(array('config' => array('allow-plugins' => array('some/plugin' => true))));