fix: don't allow invalid class names

tests/Fixtures/Suites/InvalidNames/2fa/login.test.php

@@ -0,0 +1,5 @@
+<?php
+
+// The folder name creates the namespace segment `2fa`, which starts with a number.
+
+it('never runs')->assertTrue(true);

tests/Fixtures/Suites/InvalidNames/ReservedKeyword/list.test.php

@@ -0,0 +1,5 @@
+<?php
+
+// The file name creates the class `list`, which is a PHP keyword.
+
+it('never runs')->assertTrue(true);

tests/Fixtures/Suites/InvalidNames/ReservedType/int.test.php

@@ -0,0 +1,5 @@
+<?php
+
+// The file name creates the class `int`, which is a name PHP reserves.
+
+it('never runs')->assertTrue(true);

tests/Fixtures/Suites/InvalidNames/StartsWithNumber/2fa.test.php

@@ -0,0 +1,5 @@
+<?php
+
+// The file name creates the class `2fa`, which starts with a number.
+
+it('never runs')->assertTrue(true);