diff --git a/helper/FFI/ClientTrait.php b/helper/FFI/ClientTrait.php
index ebfc7342..9322728a 100644
--- a/helper/FFI/ClientTrait.php
+++ b/helper/FFI/ClientTrait.php
@@ -8,6 +8,8 @@
 use PhpPact\Consumer\Driver\Exception\InteractionPendingNotSetException;
 use PhpPact\Consumer\Driver\Exception\PactFileNotWrittenException;
 use PhpPact\Consumer\Driver\Exception\PactNotModifiedException;
+use PhpPact\Consumer\Exception\MockServerNotStartedException;
+use PhpPact\Consumer\Exception\MockServerPactFileNotWrittenException;
 use PhpPact\FFI\ClientInterface;
 use PhpPact\Plugin\Exception\PluginNotLoadedException;
 use PHPUnit\Framework\Constraint\Constraint;
@@ -350,4 +352,81 @@ protected function expectsUsingPlugin(int $pact, string $name, ?string $version,
             });
         }
     }
+
+    protected function expectsCleanupMockServer(int $port, bool $result): void
+    {
+        $this->client
+            ->expects($this->once())
+            ->method('cleanupMockServer')
+            ->with($port)
+            ->willReturn($result);
+    }
+
+    protected function expectsMockServerMatched(int $port, bool $result): void
+    {
+        $this->client
+            ->expects($this->once())
+            ->method('mockServerMatched')
+            ->with($port)
+            ->willReturn($result);
+    }
+
+    protected function expectsMockServerMismatches(int $port, string $result, bool $matched): void
+    {
+        if (!$matched) {
+            $this->client
+                ->expects($this->once())
+                ->method('mockServerMismatches')
+                ->with($port)
+                ->willReturn($result);
+        } else {
+            $this->client
+                ->expects($this->never())
+                ->method('mockServerMismatches');
+        }
+    }
+
+    protected function expectsWritePactFile(int $port, string $directory, bool $overwrite, int $result, bool $matched): void
+    {
+        if ($matched) {
+            $this->client
+                ->expects($this->once())
+                ->method('writePactFile')
+                ->with($port, $directory, $overwrite)
+                ->willReturn($result);
+            if ($result) {
+                $this->expectException(MockServerPactFileNotWrittenException::class);
+                $this->expectExceptionMessage(match ($result) {
+                    1 => 'A general panic was caught',
+                    2 => 'The pact file was not able to be written',
+                    3 => 'A mock server with the provided port was not found',
+                    default => 'Unknown error',
+                });
+            }
+        } else {
+            $this->client
+                ->expects($this->never())
+                ->method('writePactFile');
+        }
+    }
+
+    protected function expectsCreateMockServerForTransport(int $pact, string $host, int $port, string $transport, ?string $transportConfig, int $result): void
+    {
+        $this->client
+            ->expects($this->once())
+            ->method('createMockServerForTransport')
+            ->with($pact, $host, $port, $transport, $transportConfig)
+            ->willReturn($result);
+        if ($result < 0) {
+            $this->expectException(MockServerNotStartedException::class);
+            $this->expectExceptionMessage(match ($result) {
+                -1 => 'An invalid handle was received. Handles should be created with `pactffi_new_pact`',
+                -2 => 'Transport_config is not valid JSON',
+                -3 => 'The mock server could not be started',
+                -4 => 'The method panicked',
+                -5 => 'The address is not valid',
+                default => 'Unknown error',
+            });
+        }
+    }
 }
diff --git a/src/PhpPact/Consumer/Service/MockServer.php b/src/PhpPact/Consumer/Service/MockServer.php
index b34dd9fa..996a1c7c 100644
--- a/src/PhpPact/Consumer/Service/MockServer.php
+++ b/src/PhpPact/Consumer/Service/MockServer.php
@@ -22,8 +22,7 @@ public function __construct(
 
     public function start(): void
     {
-        $port = $this->client->call(
-            'pactffi_create_mock_server_for_transport',
+        $port = $this->client->createMockServerForTransport(
             $this->pactDriver->getPact()->handle,
             $this->config->getHost(),
             $this->config->getPort(),
@@ -66,8 +65,7 @@ protected function getTransportConfig(): ?string
 
     public function writePact(): void
     {
-        $error = $this->client->call(
-            'pactffi_write_pact_file',
+        $error = $this->client->writePactFile(
             $this->config->getPort(),
             $this->config->getPactDir(),
             $this->config->getPactFileWriteMode() === PactConfigInterface::MODE_OVERWRITE
@@ -79,19 +77,20 @@ public function writePact(): void
 
     public function cleanUp(): void
     {
-        $this->client->call('pactffi_cleanup_mock_server', $this->config->getPort());
+        $success = $this->client->cleanupMockServer($this->config->getPort());
+        if (!$success) {
+            trigger_error(sprintf("Can not clean up mock server: Mock server with the given port number '%s' does not exist, or the function panics", $this->config->getPort()), E_USER_WARNING);
+        }
         $this->pactDriver->cleanUp();
     }
 
     private function isMatched(): bool
     {
-        return $this->client->call('pactffi_mock_server_matched', $this->config->getPort());
+        return $this->client->mockServerMatched($this->config->getPort());
     }
 
     private function getMismatches(): string
     {
-        $cData = $this->client->call('pactffi_mock_server_mismatches', $this->config->getPort());
-
-        return FFI::string($cData);
+        return $this->client->mockServerMismatches($this->config->getPort());
     }
 }
diff --git a/src/PhpPact/FFI/Client.php b/src/PhpPact/FFI/Client.php
index 75bf924d..6006bb2f 100644
--- a/src/PhpPact/FFI/Client.php
+++ b/src/PhpPact/FFI/Client.php
@@ -247,6 +247,59 @@ public function usingPlugin(int $pact, string $name, ?string $version): int
         return $result;
     }
 
+    public function cleanupMockServer(int $port): bool
+    {
+        $method = 'pactffi_cleanup_mock_server';
+        $result = $this->call($method, $port);
+        if (!is_bool($result)) {
+            throw new InvalidResultException(sprintf('Invalid result of "%s". Expected "boolean", but got "%s"', $method, get_debug_type($result)));
+        }
+        return $result;
+    }
+
+    public function mockServerMatched(int $port): bool
+    {
+        $method = 'pactffi_mock_server_matched';
+        $result = $this->call($method, $port);
+        if (!is_bool($result)) {
+            throw new InvalidResultException(sprintf('Invalid result of "%s". Expected "boolean", but got "%s"', $method, get_debug_type($result)));
+        }
+        return $result;
+    }
+
+    public function mockServerMismatches(int $port): string
+    {
+        $method = 'pactffi_mock_server_mismatches';
+        $result = $this->call($method, $port);
+        if ($result === null) {
+            return '';
+        }
+        if (!$result instanceof CData) {
+            throw new InvalidResultException(sprintf('Invalid result of "%s". Expected "%s", but got "%s"', $method, CData::class, get_debug_type($result)));
+        }
+        return FFI::string($result);
+    }
+
+    public function writePactFile(int $port, string $directory, bool $overwrite): int
+    {
+        $method = 'pactffi_write_pact_file';
+        $result = $this->call($method, $port, $directory, $overwrite);
+        if (!is_int($result)) {
+            throw new InvalidResultException(sprintf('Invalid result of "%s". Expected "integer", but got "%s"', $method, get_debug_type($result)));
+        }
+        return $result;
+    }
+
+    public function createMockServerForTransport(int $pact, string $host, int $port, string $transport, ?string $transportConfig): int
+    {
+        $method = 'pactffi_create_mock_server_for_transport';
+        $result = $this->call($method, $pact, $host, $port, $transport, $transportConfig);
+        if (!is_int($result)) {
+            throw new InvalidResultException(sprintf('Invalid result of "%s". Expected "integer", but got "%s"', $method, get_debug_type($result)));
+        }
+        return $result;
+    }
+
     public function getInteractionPartRequest(): int
     {
         return $this->getEnum('InteractionPart_Request');
diff --git a/src/PhpPact/FFI/ClientInterface.php b/src/PhpPact/FFI/ClientInterface.php
index 71f78a11..544fca5b 100644
--- a/src/PhpPact/FFI/ClientInterface.php
+++ b/src/PhpPact/FFI/ClientInterface.php
@@ -55,6 +55,16 @@ public function cleanupPlugins(int $pact): void;
 
     public function usingPlugin(int $pact, string $name, ?string $version): int;
 
+    public function cleanupMockServer(int $port): bool;
+
+    public function mockServerMatched(int $port): bool;
+
+    public function mockServerMismatches(int $port): string;
+
+    public function writePactFile(int $port, string $directory, bool $overwrite): int;
+
+    public function createMockServerForTransport(int $pact, string $host, int $port, string $transport, ?string $transportConfig): int;
+
     public function getInteractionPartRequest(): int;
 
     public function getInteractionPartResponse(): int;
diff --git a/tests/PhpPact/Consumer/Service/MockServerTest.php b/tests/PhpPact/Consumer/Service/MockServerTest.php
index 0da0bd90..b07f7493 100644
--- a/tests/PhpPact/Consumer/Service/MockServerTest.php
+++ b/tests/PhpPact/Consumer/Service/MockServerTest.php
@@ -2,10 +2,8 @@
 
 namespace PhpPactTest\Consumer\Service;
 
-use FFI;
 use PhpPact\Config\PactConfigInterface;
 use PhpPact\Consumer\Driver\Pact\PactDriverInterface;
-use PhpPact\Consumer\Exception\MockServerNotStartedException;
 use PhpPact\Consumer\Exception\MockServerPactFileNotWrittenException;
 use PhpPact\Consumer\Model\Pact\Pact;
 use PhpPact\Consumer\Service\MockServer;
@@ -56,21 +54,7 @@ public function testStart(int $returnedPort, bool $secure): void
             ->expects($this->once())
             ->method('getPact')
             ->willReturn(new Pact($this->pactHandle));
-        $calls = [
-            ['pactffi_create_mock_server_for_transport', $this->pactHandle, $this->host, $this->port, $this->getTransport($secure), null, $returnedPort],
-        ];
-        $this->assertClientCalls($calls);
-        if ($returnedPort < 0) {
-            $this->expectException(MockServerNotStartedException::class);
-            $this->expectExceptionMessage(match ($returnedPort) {
-                -1 => 'An invalid handle was received. Handles should be created with `pactffi_new_pact`',
-                -2 => 'Transport_config is not valid JSON',
-                -3 => 'The mock server could not be started',
-                -4 => 'The method panicked',
-                -5 => 'The address is not valid',
-                default => 'Unknown error',
-            });
-        }
+        $this->expectsCreateMockServerForTransport($this->pactHandle, $this->host, $this->port, $this->getTransport($secure), null, $returnedPort);
         $this->mockServer->start();
         $this->assertSame($returnedPort, $this->config->getPort());
     }
@@ -81,16 +65,10 @@ public function testVerify(bool $matched): void
     {
         $this->config->setPort($this->port);
         $this->config->setPactDir($this->pactDir);
-        $calls = $matched ? [
-            ['pactffi_mock_server_matched', $this->port, $matched],
-            ['pactffi_write_pact_file', $this->port, $this->pactDir, false, 0],
-            ['pactffi_cleanup_mock_server', $this->port, null],
-        ] : [
-            ['pactffi_mock_server_matched', $this->port, $matched],
-            ['pactffi_mock_server_mismatches', $this->port, FFI::new('char[1]')],
-            ['pactffi_cleanup_mock_server', $this->port, null],
-        ];
-        $this->assertClientCalls($calls);
+        $this->expectsMockServerMatched($this->port, $matched);
+        $this->expectsWritePactFile($this->port, $this->pactDir, false, 0, $matched);
+        $this->expectsMockServerMismatches($this->port, '', $matched);
+        $this->expectsCleanupMockServer($this->port, true);
         $this->pactDriver
             ->expects($this->once())
             ->method('cleanUp');
@@ -114,10 +92,7 @@ public function testWritePact(int $error, string $writeMode): void
         $this->config->setPort($this->port);
         $this->config->setPactDir($this->pactDir);
         $this->config->setPactFileWriteMode($writeMode);
-        $calls = [
-            ['pactffi_write_pact_file', $this->port, $this->pactDir, $writeMode === PactConfigInterface::MODE_OVERWRITE, $error],
-        ];
-        $this->assertClientCalls($calls);
+        $this->expectsWritePactFile($this->port, $this->pactDir, $writeMode === PactConfigInterface::MODE_OVERWRITE, $error, true);
         if ($error) {
             $this->expectException(MockServerPactFileNotWrittenException::class);
             $this->expectExceptionMessage(match ($error) {
@@ -130,13 +105,12 @@ public function testWritePact(int $error, string $writeMode): void
         $this->mockServer->writePact();
     }
 
-    public function testCleanUp(): void
+    #[TestWith([true])]
+    #[TestWith([false])]
+    public function testCleanUp(bool $success): void
     {
         $this->config->setPort($this->port);
-        $calls = [
-            ['pactffi_cleanup_mock_server', $this->port, null],
-        ];
-        $this->assertClientCalls($calls);
+        $this->expectsCleanupMockServer($this->port, $success);
         $this->pactDriver
             ->expects($this->once())
             ->method('cleanUp');
diff --git a/tests/PhpPact/FFI/ClientTest.php b/tests/PhpPact/FFI/ClientTest.php
index 5ece2e18..8c3824c1 100644
--- a/tests/PhpPact/FFI/ClientTest.php
+++ b/tests/PhpPact/FFI/ClientTest.php
@@ -165,6 +165,36 @@ public function testUsingPlugin(): void
         $this->assertSame(2, $result);
     }
 
+    public function testCleanupMockServer(): void
+    {
+        $result = $this->client->cleanupMockServer(1234);
+        $this->assertFalse($result);
+    }
+
+    public function testMockServerMatched(): void
+    {
+        $result = $this->client->mockServerMatched(1234);
+        $this->assertFalse($result);
+    }
+
+    public function testMockServerMismatches(): void
+    {
+        $result = $this->client->mockServerMismatches(1234);
+        $this->assertSame('', $result);
+    }
+
+    public function testWritePactFile(): void
+    {
+        $result = $this->client->writePactFile(1234, 'test', true);
+        $this->assertSame(3, $result);
+    }
+
+    public function testCreateMockServerForTransport(): void
+    {
+        $result = $this->client->createMockServerForTransport(1, 'localhost', 1234, 'http', null);
+        $this->assertSame(-1, $result);
+    }
+
     public function testGetInteractionPartRequest(): void
     {
         $this->assertSame(0, $this->client->getInteractionPartRequest());