diff --git a/tests/Core/File/FindExtendedClassNameTest.inc b/tests/Core/File/FindExtendedClassNameTest.inc
index aead06cd9d..dae2cd9692 100644
--- a/tests/Core/File/FindExtendedClassNameTest.inc
+++ b/tests/Core/File/FindExtendedClassNameTest.inc
@@ -1,27 +1,32 @@
 <?php
 
-namespace PHP_CodeSniffer\Tests\Core\File;
+/* testNotAClass */
+function notAClass() {}
 
-class testFECNClass {}
+/* testNonExtendedClass */
+class testFECNNonExtendedClass {}
 
-/* testExtendedClass */
+/* testExtendsUnqualifiedClass */
 class testFECNExtendedClass extends testFECNClass {}
 
-/* testNamespacedClass */
+/* testExtendsFullyQualifiedClass */
 class testFECNNamespacedClass extends \PHP_CodeSniffer\Tests\Core\File\testFECNClass {}
 
-/* testNonExtendedClass */
-class testFECNNonExtendedClass {}
+/* testExtendsPartiallyQualifiedClass */
+class testFECNQualifiedClass extends Core\File\RelativeClass {}
 
-/* testInterface */
+/* testNonExtendedInterface */
 interface testFECNInterface {}
 
-/* testInterfaceThatExtendsInterface */
+/* testInterfaceExtendsUnqualifiedInterface */
 interface testInterfaceThatExtendsInterface extends testFECNInterface{}
 
-/* testInterfaceThatExtendsFQCNInterface */
+/* testInterfaceExtendsFullyQualifiedInterface */
 interface testInterfaceThatExtendsFQCNInterface extends \PHP_CodeSniffer\Tests\Core\File\testFECNInterface{}
 
+/* testExtendedAnonClass */
+$anon = new class( $a, $b ) extends testFECNExtendedAnonClass {};
+
 /* testNestedExtendedClass */
 class testFECNNestedExtendedClass {
 	public function someMethod() {
@@ -35,3 +40,13 @@ class testFECNClassThatExtendsAndImplements extends testFECNClass implements Int
 
 /* testClassThatImplementsAndExtends */
 class testFECNClassThatImplementsAndExtends implements InterfaceA, InterfaceB extends testFECNClass {}
+
+/* testInterfaceMultiExtends */
+interface Multi extends \Package\FooInterface, \BarInterface {};
+
+/* testMissingExtendsName */
+class testMissingExtendsName extends { /* missing classname */ } // Intentional parse error.
+
+// Intentional parse error. Has to be the last test in the file.
+/* testParseError */
+class testParseError extends testFECNClass
diff --git a/tests/Core/File/FindExtendedClassNameTest.php b/tests/Core/File/FindExtendedClassNameTest.php
index c54b9cc120..be13208908 100644
--- a/tests/Core/File/FindExtendedClassNameTest.php
+++ b/tests/Core/File/FindExtendedClassNameTest.php
@@ -20,12 +20,39 @@ class FindExtendedClassNameTest extends AbstractMethodUnitTest
 {
 
 
+    /**
+     * Test getting a `false` result when a non-existent token is passed.
+     *
+     * @return void
+     */
+    public function testNonExistentToken()
+    {
+        $result = self::$phpcsFile->findExtendedClassName(100000);
+        $this->assertFalse($result);
+
+    }//end testNonExistentToken()
+
+
+    /**
+     * Test getting a `false` result when a token other than one of the supported tokens is passed.
+     *
+     * @return void
+     */
+    public function testNotAClass()
+    {
+        $token  = $this->getTargetToken('/* testNotAClass */', [T_FUNCTION]);
+        $result = self::$phpcsFile->findExtendedClassName($token);
+        $this->assertFalse($result);
+
+    }//end testNotAClass()
+
+
     /**
      * Test retrieving the name of the class being extended by another class
      * (or interface).
      *
-     * @param string $identifier Comment which precedes the test case.
-     * @param bool   $expected   Expected function output.
+     * @param string       $identifier Comment which precedes the test case.
+     * @param string|false $expected   Expected function output.
      *
      * @dataProvider dataExtendedClass
      *
@@ -45,50 +72,70 @@ public function testFindExtendedClassName($identifier, $expected)
      *
      * @see testFindExtendedClassName()
      *
-     * @return array
+     * @return array<string, array<string, string|false>>
      */
     public function dataExtendedClass()
     {
         return [
-            [
-                '/* testExtendedClass */',
-                'testFECNClass',
+            'class does not extend'                                       => [
+                'identifier' => '/* testNonExtendedClass */',
+                'expected'   => false,
+            ],
+            'class extends unqualified class'                             => [
+                'identifier' => '/* testExtendsUnqualifiedClass */',
+                'expected'   => 'testFECNClass',
+            ],
+            'class extends fully qualified class'                         => [
+                'identifier' => '/* testExtendsFullyQualifiedClass */',
+                'expected'   => '\PHP_CodeSniffer\Tests\Core\File\testFECNClass',
+            ],
+            'class extends partially qualified class'                     => [
+                'identifier' => '/* testExtendsPartiallyQualifiedClass */',
+                'expected'   => 'Core\File\RelativeClass',
+            ],
+            'interface does not extend'                                   => [
+                'identifier' => '/* testNonExtendedInterface */',
+                'expected'   => false,
+            ],
+            'interface extends unqualified interface'                     => [
+                'identifier' => '/* testInterfaceExtendsUnqualifiedInterface */',
+                'expected'   => 'testFECNInterface',
             ],
-            [
-                '/* testNamespacedClass */',
-                '\PHP_CodeSniffer\Tests\Core\File\testFECNClass',
+            'interface extends fully qualified interface'                 => [
+                'identifier' => '/* testInterfaceExtendsFullyQualifiedInterface */',
+                'expected'   => '\PHP_CodeSniffer\Tests\Core\File\testFECNInterface',
             ],
-            [
-                '/* testNonExtendedClass */',
-                false,
+            'anon class extends unqualified class'                        => [
+                'identifier' => '/* testExtendedAnonClass */',
+                'expected'   => 'testFECNExtendedAnonClass',
             ],
-            [
-                '/* testInterface */',
-                false,
+            'class does not extend but contains anon class which extends' => [
+                'identifier' => '/* testNestedExtendedClass */',
+                'expected'   => false,
             ],
-            [
-                '/* testInterfaceThatExtendsInterface */',
-                'testFECNInterface',
+            'anon class extends, nested in non-extended class'            => [
+                'identifier' => '/* testNestedExtendedAnonClass */',
+                'expected'   => 'testFECNAnonClass',
             ],
-            [
-                '/* testInterfaceThatExtendsFQCNInterface */',
-                '\PHP_CodeSniffer\Tests\Core\File\testFECNInterface',
+            'class extends and implements'                                => [
+                'identifier' => '/* testClassThatExtendsAndImplements */',
+                'expected'   => 'testFECNClass',
             ],
-            [
-                '/* testNestedExtendedClass */',
-                false,
+            'class implements and extends'                                => [
+                'identifier' => '/* testClassThatImplementsAndExtends */',
+                'expected'   => 'testFECNClass',
             ],
-            [
-                '/* testNestedExtendedAnonClass */',
-                'testFECNAnonClass',
+            'interface extends multiple interfaces (not supported)'       => [
+                'identifier' => '/* testInterfaceMultiExtends */',
+                'expected'   => '\Package\FooInterface',
             ],
-            [
-                '/* testClassThatExtendsAndImplements */',
-                'testFECNClass',
+            'parse error - extends keyword, but no class name'            => [
+                'identifier' => '/* testMissingExtendsName */',
+                'expected'   => false,
             ],
-            [
-                '/* testClassThatImplementsAndExtends */',
-                'testFECNClass',
+            'parse error - live coding - no curly braces'                 => [
+                'identifier' => '/* testParseError */',
+                'expected'   => false,
             ],
         ];