diff -up ./src/Framework/MockObject/Builder/Match.php.php8 ./src/Framework/MockObject/Builder/Match.php
--- ./src/Framework/MockObject/Builder/Match.php.php8	2020-01-08 09:45:45.000000000 +0100
+++ ./src/Framework/MockObject/Builder/Match.php	2021-03-26 14:22:46.505856216 +0100
@@ -12,7 +12,7 @@ namespace PHPUnit\Framework\MockObject\B
 /**
  * Builder interface for invocation order matches.
  */
-interface Match extends Stub
+interface Match_ extends Stub
 {
     /**
      * Defines the expectation which must occur before the current is valid.
diff -up ./src/Framework/MockObject/Builder/NamespaceMatch.php.php8 ./src/Framework/MockObject/Builder/NamespaceMatch.php
--- ./src/Framework/MockObject/Builder/NamespaceMatch.php.php8	2020-01-08 09:45:45.000000000 +0100
+++ ./src/Framework/MockObject/Builder/NamespaceMatch.php	2021-03-26 14:22:46.505856216 +0100
@@ -33,5 +33,5 @@ interface NamespaceMatch
      * @param string $id      The identification of the match builder
      * @param Match  $builder The builder which is being registered
      */
-    public function registerId($id, Match $builder);
+    public function registerId($id, Match_ $builder);
 }
diff -up ./src/Framework/MockObject/Builder/ParametersMatch.php.php8 ./src/Framework/MockObject/Builder/ParametersMatch.php
--- ./src/Framework/MockObject/Builder/ParametersMatch.php.php8	2020-01-08 09:45:45.000000000 +0100
+++ ./src/Framework/MockObject/Builder/ParametersMatch.php	2021-03-26 14:22:46.505856216 +0100
@@ -14,7 +14,7 @@ use PHPUnit\Framework\MockObject\Matcher
 /**
  * Builder interface for parameter matchers.
  */
-interface ParametersMatch extends Match
+interface ParametersMatch extends Match_
 {
     /**
      * Sets the parameters to match for, each parameter to this function will
diff -up ./src/Framework/MockObject/InvocationMocker.php.php8 ./src/Framework/MockObject/InvocationMocker.php
--- ./src/Framework/MockObject/InvocationMocker.php.php8	2020-01-08 09:45:45.000000000 +0100
+++ ./src/Framework/MockObject/InvocationMocker.php	2021-03-26 14:22:46.505856216 +0100
@@ -12,7 +12,7 @@ namespace PHPUnit\Framework\MockObject;
 use Exception;
 use PHPUnit\Framework\ExpectationFailedException;
 use PHPUnit\Framework\MockObject\Builder\InvocationMocker as BuilderInvocationMocker;
-use PHPUnit\Framework\MockObject\Builder\Match;
+use PHPUnit\Framework\MockObject\Builder\Match_;
 use PHPUnit\Framework\MockObject\Builder\NamespaceMatch;
 use PHPUnit\Framework\MockObject\Matcher\DeferredError;
 use PHPUnit\Framework\MockObject\Matcher\Invocation as MatcherInvocation;
@@ -82,7 +82,7 @@ class InvocationMocker implements Invoka
     /**
      * @throws RuntimeException
      */
-    public function registerId($id, Match $builder): void
+    public function registerId($id, Match_ $builder): void
     {
         if (isset($this->builderMap[$id])) {
             throw new RuntimeException(
diff -up ./src/Framework/MockObject/MockMethod.php.php8 ./src/Framework/MockObject/MockMethod.php
--- ./src/Framework/MockObject/MockMethod.php.php8	2020-01-08 09:45:45.000000000 +0100
+++ ./src/Framework/MockObject/MockMethod.php	2021-03-26 14:23:49.737575694 +0100
@@ -12,6 +12,7 @@ namespace PHPUnit\Framework\MockObject;
 use ReflectionClass;
 use ReflectionException;
 use ReflectionMethod;
+use ReflectionNamedType;
 use Text_Template;
 
 final class MockMethod
@@ -269,7 +270,7 @@ final class MockMethod
      *
      * @throws RuntimeException
      */
-    private static function getMethodParameters(ReflectionMethod $method, bool $forCall = false): string
+    private static function getMethodParametersForDeclaration(ReflectionMethod $method): string
     {
         $parameters = [];
 
@@ -283,63 +284,38 @@ final class MockMethod
                 $name = '$arg' . $i;
             }
 
-            if ($parameter->isVariadic()) {
-                if ($forCall) {
-                    continue;
-                }
-
-                $name = '...' . $name;
-            }
-
             $nullable        = '';
             $default         = '';
             $reference       = '';
             $typeDeclaration = '';
+            $type            = null;
+            $typeName        = null;
 
-            if (!$forCall) {
-                if ($parameter->hasType() && $parameter->allowsNull()) {
-                    $nullable = '?';
+            if ($parameter->hasType()) {
+                $type = $parameter->getType();
+
+                if ($type instanceof ReflectionNamedType) {
+                    $typeName = $type->getName();
                 }
+            }
+
+            if ($parameter->isVariadic()) {
+                $name = '...' . $name;
+            } elseif ($parameter->isDefaultValueAvailable()) {
+                $default = ' = ' . var_export($parameter->getDefaultValue(), true);
+            } elseif ($parameter->isOptional()) {
+                $default = ' = null';
+            }
 
-                if ($parameter->hasType() && $parameter->getType()->getName() !== 'self') {
-                    $typeDeclaration = $parameter->getType()->getName() . ' ';
-                } else {
-                    try {
-                        $class = $parameter->getClass();
-                    } catch (ReflectionException $e) {
-                        throw new RuntimeException(
-                            \sprintf(
-                                'Cannot mock %s::%s() because a class or ' .
-                                'interface used in the signature is not loaded',
-                                $method->getDeclaringClass()->getName(),
-                                $method->getName()
-                            ),
-                            0,
-                            $e
-                        );
-                    }
-
-                    if ($class !== null) {
-                        $typeDeclaration = $class->getName() . ' ';
-                    }
+            if ($type !== null) {
+                if ($typeName !== 'mixed' && $parameter->allowsNull()) {
+                    $nullable = '?';
                 }
 
-                if (!$parameter->isVariadic()) {
-                    if ($parameter->isDefaultValueAvailable()) {
-                        try {
-                            $value = \var_export($parameter->getDefaultValue(), true);
-                        } catch (\ReflectionException $e) {
-                            throw new RuntimeException(
-                                $e->getMessage(),
-                                (int) $e->getCode(),
-                                $e
-                            );
-                        }
-
-                        $default = ' = ' . $value;
-                    } elseif ($parameter->isOptional()) {
-                        $default = ' = null';
-                    }
+                if ($typeName === 'self') {
+                    $typeDeclaration = $method->getDeclaringClass()->getName() . ' ';
+                } elseif ($typeName !== null) {
+                    $typeDeclaration = $typeName . ' ';
                 }
             }
 
@@ -350,6 +326,53 @@ final class MockMethod
             $parameters[] = $nullable . $typeDeclaration . $reference . $name . $default;
         }
 
-        return \implode(', ', $parameters);
+        return implode(', ', $parameters);
+    }
+
+    /**
+     * Returns the parameters of a function or method.
+     *
+     * @throws ReflectionException
+     */
+    private static function getMethodParametersForCall(ReflectionMethod $method): string
+    {
+        $parameters = [];
+
+        foreach ($method->getParameters() as $i => $parameter) {
+            $name = '$' . $parameter->getName();
+
+            /* Note: PHP extensions may use empty names for reference arguments
+             * or "..." for methods taking a variable number of arguments.
+             */
+            if ($name === '$' || $name === '$...') {
+                $name = '$arg' . $i;
+            }
+
+            if ($parameter->isVariadic()) {
+                continue;
+            }
+
+            if ($parameter->isPassedByReference()) {
+                $parameters[] = '&' . $name;
+            } else {
+                $parameters[] = $name;
+            }
+        }
+
+        return implode(', ', $parameters);
+    }
+
+
+    /**
+     * Returns the parameters of a function or method.
+     *
+     * @throws RuntimeException
+     */
+    private static function getMethodParameters(ReflectionMethod $method, bool $forCall = false): string
+    {
+        if ($forCall) {
+            return self::getMethodParametersForCall($method);
+        }
+        return self::getMethodParametersForDeclaration($method);
     }
 }
diff -up ./tests/_files/SingletonClass.php.php8 ./tests/_files/SingletonClass.php
--- ./tests/_files/SingletonClass.php.php8	2020-01-08 09:45:45.000000000 +0100
+++ ./tests/_files/SingletonClass.php	2021-03-26 14:22:46.505856216 +0100
@@ -17,11 +17,11 @@ class SingletonClass
     {
     }
 
-    private function __sleep()
+    function __sleep()
     {
     }
 
-    private function __wakeup()
+    function __wakeup()
     {
     }
 
diff -up ./tests/unit/Framework/Constraint/IsTypeTest.php.php8 ./tests/unit/Framework/Constraint/IsTypeTest.php
--- ./tests/unit/Framework/Constraint/IsTypeTest.php.php8	2020-01-08 09:45:45.000000000 +0100
+++ ./tests/unit/Framework/Constraint/IsTypeTest.php	2021-03-26 14:22:46.505856216 +0100
@@ -74,7 +74,7 @@ EOF
 
         $this->assertTrue($constraint->evaluate($resource, '', true));
 
-        @\fclose($resource);
+        if (is_resource($resource)) @\fclose($resource);
     }
 
     public function resources()
diff -up ./tests/unit/Framework/Constraint/JsonMatchesErrorMessageProviderTest.php.php8 ./tests/unit/Framework/Constraint/JsonMatchesErrorMessageProviderTest.php
--- ./tests/unit/Framework/Constraint/JsonMatchesErrorMessageProviderTest.php.php8	2020-01-08 09:45:45.000000000 +0100
+++ ./tests/unit/Framework/Constraint/JsonMatchesErrorMessageProviderTest.php	2021-03-26 14:22:46.505856216 +0100
@@ -17,7 +17,7 @@ class JsonMatchesErrorMessageProviderTes
     {
         return [
             'JSON_ERROR_NONE'  => [
-                null, 'json_error_none', '',
+                null, \JSON_ERROR_NONE, '',
             ],
             'JSON_ERROR_DEPTH' => [
                 'Maximum stack depth exceeded', \JSON_ERROR_DEPTH, '',