diff --git a/core/composer.json b/core/composer.json
index a6d52d1082..e5f39e6c54 100644
--- a/core/composer.json
+++ b/core/composer.json
@@ -192,13 +192,10 @@
     "autoload": {
         "psr-4": {
             "Drupal\\Core\\": "lib/Drupal/Core",
-            "Drupal\\Component\\": "lib/Drupal/Component",
             "Drupal\\Driver\\": "../drivers/lib/Drupal/Driver"
         },
         "classmap": [
             "lib/Drupal.php",
-            "lib/Drupal/Component/Utility/Timer.php",
-            "lib/Drupal/Component/Utility/Unicode.php",
             "lib/Drupal/Core/Database/Database.php",
             "lib/Drupal/Core/DrupalKernel.php",
             "lib/Drupal/Core/DrupalKernelInterface.php",
diff --git a/core/lib/Drupal/Component/Annotation/composer.json b/core/lib/Drupal/Component/Annotation/composer.json
index 51e7d25b00..6e701b7405 100644
--- a/core/lib/Drupal/Component/Annotation/composer.json
+++ b/core/lib/Drupal/Component/Annotation/composer.json
@@ -15,6 +15,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\Annotation\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/Assertion/composer.json b/core/lib/Drupal/Component/Assertion/composer.json
index cdc8c928fb..fbcf2e9d1c 100644
--- a/core/lib/Drupal/Component/Assertion/composer.json
+++ b/core/lib/Drupal/Component/Assertion/composer.json
@@ -10,6 +10,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\Assertion\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/Bridge/composer.json b/core/lib/Drupal/Component/Bridge/composer.json
index 19c8a3b1d3..abb5b44ff5 100644
--- a/core/lib/Drupal/Component/Bridge/composer.json
+++ b/core/lib/Drupal/Component/Bridge/composer.json
@@ -11,6 +11,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\Bridge\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/ClassFinder/composer.json b/core/lib/Drupal/Component/ClassFinder/composer.json
index c5a97b09f1..afd2965a14 100644
--- a/core/lib/Drupal/Component/ClassFinder/composer.json
+++ b/core/lib/Drupal/Component/ClassFinder/composer.json
@@ -11,6 +11,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\ClassFinder\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/Datetime/composer.json b/core/lib/Drupal/Component/Datetime/composer.json
index 6b7f89f00b..daddf8f448 100644
--- a/core/lib/Drupal/Component/Datetime/composer.json
+++ b/core/lib/Drupal/Component/Datetime/composer.json
@@ -11,6 +11,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\Datetime\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/DependencyInjection/composer.json b/core/lib/Drupal/Component/DependencyInjection/composer.json
index 846034affa..b67e10076f 100644
--- a/core/lib/Drupal/Component/DependencyInjection/composer.json
+++ b/core/lib/Drupal/Component/DependencyInjection/composer.json
@@ -20,6 +20,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\DependencyInjection\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/Diff/composer.json b/core/lib/Drupal/Component/Diff/composer.json
index fc9e1cd675..b4cbbd3ae5 100644
--- a/core/lib/Drupal/Component/Diff/composer.json
+++ b/core/lib/Drupal/Component/Diff/composer.json
@@ -11,6 +11,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\Diff\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/Discovery/composer.json b/core/lib/Drupal/Component/Discovery/composer.json
index 4de189402a..ee0d9eea3a 100644
--- a/core/lib/Drupal/Component/Discovery/composer.json
+++ b/core/lib/Drupal/Component/Discovery/composer.json
@@ -12,6 +12,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\Discovery\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/EventDispatcher/composer.json b/core/lib/Drupal/Component/EventDispatcher/composer.json
index cfbcc72e3f..c368a995e2 100644
--- a/core/lib/Drupal/Component/EventDispatcher/composer.json
+++ b/core/lib/Drupal/Component/EventDispatcher/composer.json
@@ -12,6 +12,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\EventDispatcher\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/FileCache/composer.json b/core/lib/Drupal/Component/FileCache/composer.json
index 86e33a5f91..379ceb7bfe 100644
--- a/core/lib/Drupal/Component/FileCache/composer.json
+++ b/core/lib/Drupal/Component/FileCache/composer.json
@@ -10,6 +10,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\FileCache\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/FileSystem/composer.json b/core/lib/Drupal/Component/FileSystem/composer.json
index 528bb0744a..d1ff9ef8d0 100644
--- a/core/lib/Drupal/Component/FileSystem/composer.json
+++ b/core/lib/Drupal/Component/FileSystem/composer.json
@@ -10,6 +10,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\FileSystem\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/Gettext/composer.json b/core/lib/Drupal/Component/Gettext/composer.json
index 87f500a108..6c0c5f8bbc 100644
--- a/core/lib/Drupal/Component/Gettext/composer.json
+++ b/core/lib/Drupal/Component/Gettext/composer.json
@@ -15,6 +15,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\Gettext\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/Graph/composer.json b/core/lib/Drupal/Component/Graph/composer.json
index e8f645fd20..3b8a0ab617 100644
--- a/core/lib/Drupal/Component/Graph/composer.json
+++ b/core/lib/Drupal/Component/Graph/composer.json
@@ -10,6 +10,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\Graph\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/HttpFoundation/composer.json b/core/lib/Drupal/Component/HttpFoundation/composer.json
index 910a648a21..bc4a594c5d 100644
--- a/core/lib/Drupal/Component/HttpFoundation/composer.json
+++ b/core/lib/Drupal/Component/HttpFoundation/composer.json
@@ -11,6 +11,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\HttpFoundation\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/PhpStorage/composer.json b/core/lib/Drupal/Component/PhpStorage/composer.json
index 614652a95c..3c3f04ad03 100644
--- a/core/lib/Drupal/Component/PhpStorage/composer.json
+++ b/core/lib/Drupal/Component/PhpStorage/composer.json
@@ -10,6 +10,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\PhpStorage\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/Plugin/composer.json b/core/lib/Drupal/Component/Plugin/composer.json
index 77f02d6fb1..516b135f95 100644
--- a/core/lib/Drupal/Component/Plugin/composer.json
+++ b/core/lib/Drupal/Component/Plugin/composer.json
@@ -11,7 +11,10 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\Plugin\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   },
   "suggest": {
     "symfony/validator": "Leveraged in the use of context aware plugins."
diff --git a/core/lib/Drupal/Component/ProxyBuilder/composer.json b/core/lib/Drupal/Component/ProxyBuilder/composer.json
index 52fbdb8065..cc98ecc38c 100644
--- a/core/lib/Drupal/Component/ProxyBuilder/composer.json
+++ b/core/lib/Drupal/Component/ProxyBuilder/composer.json
@@ -10,6 +10,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\ProxyBuilder\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/Render/composer.json b/core/lib/Drupal/Component/Render/composer.json
index 9e44b2dd39..b9fe820a31 100644
--- a/core/lib/Drupal/Component/Render/composer.json
+++ b/core/lib/Drupal/Component/Render/composer.json
@@ -11,6 +11,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\Render\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/Serialization/composer.json b/core/lib/Drupal/Component/Serialization/composer.json
index 3439f58639..bbf7ccf83a 100644
--- a/core/lib/Drupal/Component/Serialization/composer.json
+++ b/core/lib/Drupal/Component/Serialization/composer.json
@@ -11,6 +11,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\Serialization\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/Transliteration/composer.json b/core/lib/Drupal/Component/Transliteration/composer.json
index abdce4fc81..0da2b5d63d 100644
--- a/core/lib/Drupal/Component/Transliteration/composer.json
+++ b/core/lib/Drupal/Component/Transliteration/composer.json
@@ -11,6 +11,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\Transliteration\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/Utility/composer.json b/core/lib/Drupal/Component/Utility/composer.json
index 3b8b5de5b8..2f24e6aef5 100644
--- a/core/lib/Drupal/Component/Utility/composer.json
+++ b/core/lib/Drupal/Component/Utility/composer.json
@@ -12,6 +12,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\Utility\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }
diff --git a/core/lib/Drupal/Component/Uuid/composer.json b/core/lib/Drupal/Component/Uuid/composer.json
index 8e9cced871..78a4ddb2c4 100644
--- a/core/lib/Drupal/Component/Uuid/composer.json
+++ b/core/lib/Drupal/Component/Uuid/composer.json
@@ -15,6 +15,9 @@
   "autoload": {
     "psr-4": {
       "Drupal\\Component\\Uuid\\": ""
-    }
+    },
+    "exclude-from-classmap": [
+      "/Tests/"
+    ]
   }
 }