From 40833cef376be4e904e28172e844565514912995 Mon Sep 17 00:00:00 2001
From: Dennis de Greef <github@link0.net>
Date: Sun, 30 Apr 2017 00:54:34 +0200
Subject: [PATCH 1/4] Add a few tests

---
 .travis.yml                                   |  1 +
 src/Middleware/DebugMiddleware.php            | 10 ++-
 src/Middleware/RequestIdMiddleware.php        |  7 ++
 .../ResponseSignatureMiddleware.php           |  1 -
 tests/unit/Domain/Keypair/PrivateKeyTest.php  | 33 ++++++++
 tests/unit/Domain/Keypair/PublicKeyTest.php   | 35 ++++++++
 tests/unit/Environment/ProductionTest.php     | 36 ++++++++
 tests/unit/Environment/SandboxTest.php        | 36 ++++++++
 tests/unit/Middleware/DebugMiddlewareTest.php | 65 +++++++++++++++
 .../Middleware/RequestIdMiddlewareTest.php    | 62 ++++++++++++++
 .../RequestSignatureMiddlewareTest.php        | 55 +++++++++++++
 .../ResponseSignatureMiddlewareTest.php       | 82 +++++++++++++++++++
 12 files changed, 419 insertions(+), 4 deletions(-)
 create mode 100644 tests/unit/Domain/Keypair/PrivateKeyTest.php
 create mode 100644 tests/unit/Domain/Keypair/PublicKeyTest.php
 create mode 100644 tests/unit/Environment/ProductionTest.php
 create mode 100644 tests/unit/Environment/SandboxTest.php
 create mode 100644 tests/unit/Middleware/DebugMiddlewareTest.php
 create mode 100644 tests/unit/Middleware/RequestIdMiddlewareTest.php
 create mode 100644 tests/unit/Middleware/RequestSignatureMiddlewareTest.php
 create mode 100644 tests/unit/Middleware/ResponseSignatureMiddlewareTest.php

diff --git a/.travis.yml b/.travis.yml
index 911350c..780fc76 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -18,4 +18,5 @@ before_script:
 
 script:
   - composer run phpcs
+  - ./vendor/bin/phpunit
   - composer run phpstan
diff --git a/src/Middleware/DebugMiddleware.php b/src/Middleware/DebugMiddleware.php
index bde545d..509ce00 100644
--- a/src/Middleware/DebugMiddleware.php
+++ b/src/Middleware/DebugMiddleware.php
@@ -4,6 +4,7 @@
 
 use GuzzleHttp\Middleware;
 use GuzzleHttp\Promise\FulfilledPromise;
+use GuzzleHttp\Promise\PromiseInterface;
 use Psr\Http\Message\RequestInterface;
 use Psr\Http\Message\ResponseInterface;
 
@@ -47,9 +48,12 @@ public static function request()
      */
     public static function response()
     {
-        return function (RequestInterface $request, $options, FulfilledPromise $responsePromise) {
-            $responsePromise->then(function (ResponseInterface $response) {
-                echo chr(27) . '[33m' . "RESPONSE: HTTP/" . $response->getProtocolVersion() . ' ' . $response->getStatusCode() . ' ' . $response->getReasonPhrase() . chr(27) . "[0m\n";
+        return function (RequestInterface $request, $options, PromiseInterface $responsePromise) {
+            return $responsePromise->then(function (ResponseInterface $response) {
+                echo chr(27) . '[33m' . "RESPONSE: HTTP/" .
+                    $response->getProtocolVersion() . ' ' .
+                    $response->getStatusCode() . ' ' .
+                    $response->getReasonPhrase() . chr(27) . "[0m\n";
 
                 foreach ($response->getHeaders() as $key => $headers) {
                     foreach ($headers as $header) {
diff --git a/src/Middleware/RequestIdMiddleware.php b/src/Middleware/RequestIdMiddleware.php
index 7857fbe..c22622a 100644
--- a/src/Middleware/RequestIdMiddleware.php
+++ b/src/Middleware/RequestIdMiddleware.php
@@ -8,7 +8,14 @@
 
 final class RequestIdMiddleware
 {
+    /**
+     * @var string
+     */
     private $sessionToken;
+
+    /**
+     * @param string $sessionToken
+     */
     public function __construct($sessionToken)
     {
         $this->sessionToken = $sessionToken;
diff --git a/src/Middleware/ResponseSignatureMiddleware.php b/src/Middleware/ResponseSignatureMiddleware.php
index 091ba16..3824a8b 100644
--- a/src/Middleware/ResponseSignatureMiddleware.php
+++ b/src/Middleware/ResponseSignatureMiddleware.php
@@ -58,7 +58,6 @@ public function __invoke(ResponseInterface $response)
 
             $signatureData .= "\n\n";
             $signatureData .= (string) $response->getBody();
-
             $rawSignature = base64_decode($serverSignature);
             $verify = openssl_verify($signatureData, $rawSignature, $this->publicKey, self::SIGNATURE_ALGORITHM);
             if ($verify !== 1) {
diff --git a/tests/unit/Domain/Keypair/PrivateKeyTest.php b/tests/unit/Domain/Keypair/PrivateKeyTest.php
new file mode 100644
index 0000000..93fdb6d
--- /dev/null
+++ b/tests/unit/Domain/Keypair/PrivateKeyTest.php
@@ -0,0 +1,33 @@
+<?php
+
+namespace Link0\Bunq\Tests\Domain\Keypair;
+
+use Link0\Bunq\Domain\Keypair\PrivateKey;
+use PHPUnit\Framework\TestCase;
+
+final class PrivateKeyTest extends TestCase
+{
+    /**
+     * @expectedException \InvalidArgumentException
+     * @expectedExceptionMessage Invalid PrivateKey format. Please use a shielded format
+     */
+    public function test_that_private_key_must_be_pem_formatted()
+    {
+        $key = explode("\n", TEST_PRIVATE_KEY);
+        array_shift($key); // -----BEGIN PRIVATE KEY -----
+        array_pop($key);   // -----END PRIVATE KEY -----
+        new PrivateKey(implode("\n", $key));
+    }
+
+    public function test_that_private_key_is_castable_to_string()
+    {
+        $key = new PrivateKey(TEST_PRIVATE_KEY);
+        $this->assertEquals(TEST_PRIVATE_KEY, (string)$key);
+    }
+
+    public function test_that_actual_key_is_stripped_from_debug_information()
+    {
+        $key = new PrivateKey(TEST_PRIVATE_KEY);
+        $this->assertContains('***PRIVATE KEY***', print_r($key, true));
+    }
+}
diff --git a/tests/unit/Domain/Keypair/PublicKeyTest.php b/tests/unit/Domain/Keypair/PublicKeyTest.php
new file mode 100644
index 0000000..86ff891
--- /dev/null
+++ b/tests/unit/Domain/Keypair/PublicKeyTest.php
@@ -0,0 +1,35 @@
+<?php
+
+namespace Link0\Bunq\Tests\Domain\Keypair;
+
+use Link0\Bunq\Domain\Keypair\PublicKey;
+use PHPUnit\Framework\TestCase;
+
+final class PublicKeyTest extends TestCase
+{
+    /**
+     * @expectedException \InvalidArgumentException
+     * @expectedExceptionMessage Invalid PublicKey format. Please use a shielded format
+     */
+    public function test_that_private_key_must_be_pem_formatted()
+    {
+        $key = explode("\n", TEST_PUBLIC_KEY);
+        array_shift($key); // -----BEGIN PUBLIC KEY -----
+        array_pop($key);   // -----END PUBLIC KEY -----
+        new PublicKey(implode("\n", $key));
+    }
+
+    public function test_that_private_key_is_castable_to_string()
+    {
+        $key = new PublicKey(TEST_PUBLIC_KEY);
+        $this->assertSame(TEST_PUBLIC_KEY, (string)$key);
+    }
+
+    public function test_that_public_key_can_be_made_from_server_response()
+    {
+        $key = PublicKey::fromServerPublicKey([
+            'server_public_key' => TEST_PUBLIC_KEY
+        ]);
+        $this->assertEquals(TEST_PUBLIC_KEY, $key);
+    }
+}
diff --git a/tests/unit/Environment/ProductionTest.php b/tests/unit/Environment/ProductionTest.php
new file mode 100644
index 0000000..60daab3
--- /dev/null
+++ b/tests/unit/Environment/ProductionTest.php
@@ -0,0 +1,36 @@
+<?php declare(strict_types=1);
+
+namespace Link0\Bunq\Tests\Environment;
+
+use Link0\Bunq\Environment\Production;
+use PHPUnit\Framework\TestCase;
+
+final class ProductionTest extends TestCase
+{
+    public function test_that_production_is_not_in_debug_mode_by_default()
+    {
+        $this->assertFalse((new Production())->inDebugMode());
+    }
+
+    public function test_that_production_can_be_switched_to_debug_mode()
+    {
+        $debug = true;
+        $this->assertTrue((new Production($debug))->inDebugMode());
+    }
+
+    public function test_that_version_is_one()
+    {
+        $this->assertEquals(Production::VERSION, (new Production())->version());
+    }
+
+    public function test_that_service_url_equals_constant()
+    {
+        $this->assertEquals(Production::SERVICE_URL, (new Production())->serviceUrl());
+    }
+
+    public function test_that_endpoint_aggregates_other_variables()
+    {
+        $env = new Production();
+        $this->assertEquals($env->serviceUrl() . '/' . $env->version() . '/', $env->endpoint());
+    }
+}
diff --git a/tests/unit/Environment/SandboxTest.php b/tests/unit/Environment/SandboxTest.php
new file mode 100644
index 0000000..a60df90
--- /dev/null
+++ b/tests/unit/Environment/SandboxTest.php
@@ -0,0 +1,36 @@
+<?php declare(strict_types=1);
+
+namespace Link0\Bunq\Tests\Environment;
+
+use Link0\Bunq\Environment\Sandbox;
+use PHPUnit\Framework\TestCase;
+
+final class SandboxTest extends TestCase
+{
+    public function test_that_sandbox_is_not_in_debug_mode_by_default()
+    {
+        $this->assertFalse((new Sandbox())->inDebugMode());
+    }
+
+    public function test_that_sandbox_can_be_switched_to_debug_mode()
+    {
+        $debug = true;
+        $this->assertTrue((new Sandbox($debug))->inDebugMode());
+    }
+
+    public function test_that_version_is_one()
+    {
+        $this->assertEquals(Sandbox::VERSION, (new Sandbox())->version());
+    }
+
+    public function test_that_service_url_equals_constant()
+    {
+        $this->assertEquals(Sandbox::SERVICE_URL, (new Sandbox())->serviceUrl());
+    }
+
+    public function test_that_endpoint_aggregates_other_variables()
+    {
+        $env = new Sandbox();
+        $this->assertEquals($env->serviceUrl() . '/' . $env->version() . '/', $env->endpoint());
+    }
+}
diff --git a/tests/unit/Middleware/DebugMiddlewareTest.php b/tests/unit/Middleware/DebugMiddlewareTest.php
new file mode 100644
index 0000000..7e88820
--- /dev/null
+++ b/tests/unit/Middleware/DebugMiddlewareTest.php
@@ -0,0 +1,65 @@
+<?php declare(strict_types=1);
+
+namespace Link0\Bunq\Tests\Middleware;
+
+use GuzzleHttp\Promise\FulfilledPromise;
+use Link0\Bunq\Middleware\DebugMiddleware;
+use Mockery;
+use PHPUnit\Framework\TestCase;
+use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\ResponseInterface;
+
+final class DebugMiddlewareTest extends TestCase
+{
+    public function test_that_requests_can_be_represented_as_debug_output()
+    {
+        $request = Mockery::mock(RequestInterface::class);
+        $request->shouldReceive('getMethod')->andReturn('GET');
+        $request->shouldReceive('getRequestTarget')->andReturn('/request/target');
+        $request->shouldReceive('getHeaders')->andReturn([
+            'SomeHeader' => ['SomeValue', 'SomeOtherValue'],
+        ]);
+        $request->shouldReceive('getBody')->andReturn('{"foo": "bar"}');
+
+        $requestMiddleware = DebugMiddleware::request();
+
+        ob_start();
+        $requestMiddleware($request);
+        $actual = ob_get_clean();
+
+        // Assert it contains all the desired information
+        $this->assertContains('REQUEST', $actual);
+        $this->assertContains('GET', $actual);
+        $this->assertContains('/request/target', $actual);
+        $this->assertContains('SomeHeader: SomeValue', $actual);
+        $this->assertContains('SomeHeader: SomeOtherValue', $actual);
+        $this->assertContains('{"foo": "bar"}', $actual);
+        $this->assertContains('[foo] => bar', $actual);
+    }
+
+    public function test_that_responses_can_be_represented_as_debug_output()
+    {
+        $request = Mockery::mock(RequestInterface::class);
+        $response = Mockery::mock(ResponseInterface::class);
+
+        $response->shouldReceive('getProtocolVersion')->andReturn('1.1');
+        $response->shouldReceive('getStatusCode')->andReturn('200');
+        $response->shouldReceive('getReasonPhrase')->andReturn('OK');
+        $response->shouldReceive('getBody')->andReturn('{"foo": "bar"}');
+        $response->shouldReceive('getHeaders')->andReturn([
+            'Foo' => ['Bar', 'Baz']
+        ]);
+
+        $promise = new FulfilledPromise($response);
+        $responseMiddleware = DebugMiddleware::response();
+
+        ob_start();
+        $responseMiddleware($request, [], $promise)->wait();
+        $actual = ob_get_clean();
+
+        $this->assertContains('RESPONSE: HTTP/1.1 200 OK', $actual);
+        $this->assertContains('Foo: Bar', $actual);
+        $this->assertContains('Foo: Baz', $actual);
+        $this->assertContains('[foo] => bar', $actual);
+    }
+}
diff --git a/tests/unit/Middleware/RequestIdMiddlewareTest.php b/tests/unit/Middleware/RequestIdMiddlewareTest.php
new file mode 100644
index 0000000..a9da838
--- /dev/null
+++ b/tests/unit/Middleware/RequestIdMiddlewareTest.php
@@ -0,0 +1,62 @@
+<?php declare(strict_types=1);
+
+namespace Link0\Bunq\Tests\Middleware;
+
+use GuzzleHttp\Psr7\Request;
+use Link0\Bunq\Middleware\RequestIdMiddleware;
+use Mockery;
+use Mockery\MockInterface;
+use PHPUnit\Framework\TestCase;
+
+final class RequestIdMiddlewareTest extends TestCase
+{
+    /**
+     * @const SESSION_TOKEN
+     */
+    const SESSION_TOKEN = 'some_session_token';
+
+    /**
+     * @var Request|MockInterface
+     */
+    private $request;
+
+    public function setUp()
+    {
+        $this->request = Mockery::mock(Request::class);
+        $this->request->shouldReceive('getMethod')->andReturn('GET');
+        $this->request->shouldReceive('getUri')->andReturn('/');
+        $this->request->shouldReceive('getBody')->andReturn('');
+        $this->middleware = new RequestIdMiddleware(self::SESSION_TOKEN);
+    }
+
+    public function test_that_request_id_is_generated_if_not_provided()
+    {
+        $this->request->shouldReceive('getHeaders')->andReturn([]);
+        $request = ($this->middleware)($this->request, []);
+        $requestId = $request->getHeader('X-Bunq-Client-Request-Id')[0];
+        // UUID's are always 36 characters
+        $this->assertEquals(36, strlen($requestId));
+    }
+
+    public function test_that_request_id_can_be_overridden()
+    {
+        $expected = 'foo';
+        $this->request->shouldReceive('getHeaders')->andReturn([]);
+        $request = ($this->middleware)($this->request, [
+            'request-id' => $expected,
+        ]);
+        $requestId = $request->getHeader('X-Bunq-Client-Request-Id')[0];
+        $this->assertSame($expected, $requestId);
+    }
+
+    public function test_that_session_token_can_be_overridden()
+    {
+        $expected = 'foo';
+        $this->request->shouldReceive('getHeaders')->andReturn([
+            'X-Bunq-Client-Authentication' => [$expected],
+        ]);
+        $request = ($this->middleware)($this->request, []);
+        $authentication = $request->getHeader('X-Bunq-Client-Authentication')[0];
+        $this->assertSame($expected, $authentication);
+    }
+}
diff --git a/tests/unit/Middleware/RequestSignatureMiddlewareTest.php b/tests/unit/Middleware/RequestSignatureMiddlewareTest.php
new file mode 100644
index 0000000..c93d91d
--- /dev/null
+++ b/tests/unit/Middleware/RequestSignatureMiddlewareTest.php
@@ -0,0 +1,55 @@
+<?php declare(strict_types=1);
+
+namespace Link0\Bunq\Tests\Middleware;
+
+use GuzzleHttp\Psr7\Request;
+use Link0\Bunq\Domain\Keypair\PrivateKey;
+use Link0\Bunq\Middleware\RequestSignatureMiddleware;
+use Mockery;
+use PHPUnit\Framework\TestCase;
+use Psr\Http\Message\RequestInterface;
+
+final class RequestSignatureMiddlewareTest extends TestCase
+{
+    public function test_request_signing()
+    {
+        $privateKey = new PrivateKey(TEST_PRIVATE_KEY);
+        $middleware = new RequestSignatureMiddleware($privateKey);
+
+        $request = Mockery::mock(RequestInterface::class);
+
+        $headers = [
+            'X-Bunq-Testing' => ['Foo']
+        ];
+
+        $request
+            ->shouldReceive('getHeaders')
+            ->withNoArgs()
+            ->andReturn($headers)
+        ;
+        $request
+            ->shouldReceive('getMethod')
+            ->withNoArgs()
+            ->andReturn('GET')
+        ;
+        $request
+            ->shouldReceive('getRequestTarget')
+            ->withNoArgs()
+            ->andReturn('/')
+        ;
+
+        $request->shouldReceive('getUri')->andReturn('foo');
+
+        $request
+            ->shouldReceive('getBody')
+            ->withNoArgs()
+            ->andReturn('{}');
+
+        /** @var Request $response */
+        $response = $middleware($request);
+
+        $signatureHeader = $response->getHeader('X-Bunq-Client-Signature');
+        $this->assertCount(1, $signatureHeader);
+        $this->assertArrayHasKey(0, $signatureHeader);
+    }
+}
diff --git a/tests/unit/Middleware/ResponseSignatureMiddlewareTest.php b/tests/unit/Middleware/ResponseSignatureMiddlewareTest.php
new file mode 100644
index 0000000..7750b85
--- /dev/null
+++ b/tests/unit/Middleware/ResponseSignatureMiddlewareTest.php
@@ -0,0 +1,82 @@
+<?php declare(strict_types=1);
+
+namespace Link0\Bunq\Tests\Middleware;
+
+use Link0\Bunq\Domain\Keypair\PublicKey;
+use Link0\Bunq\Middleware\ResponseSignatureMiddleware;
+use Mockery;
+use Mockery\MockInterface;
+use PHPUnit\Framework\TestCase;
+use Psr\Http\Message\ResponseInterface;
+
+final class ResponseSignatureMiddlewareTest extends TestCase
+{
+    /**
+     * @var ResponseSignatureMiddleware
+     */
+    private $middleware;
+
+    /**
+     * @var ResponseInterface|MockInterface
+     */
+    private $response;
+
+    public function setUp()
+    {
+        $this->middleware = new ResponseSignatureMiddleware(
+            new PublicKey(TEST_PUBLIC_KEY)
+        );
+        $this->response = Mockery::mock(ResponseInterface::class);
+    }
+
+    public function test_that_nothing_is_verified_when_signature_header_missing()
+    {
+        $this->response
+            ->shouldReceive('getHeader')
+            ->withArgs(['X-Bunq-Server-Signature'])
+            ->andReturn([]);
+        $response = ($this->middleware)($this->response);
+        $this->assertSame($response, $this->response);
+    }
+
+    public function test_that_headers_are_verified_when_signature_present()
+    {
+        $statusCode = 200;
+        $body = '{}';
+
+        $headers = [
+            'X-Bunq-Server-Signature' => ['chicken_egg_scenario'],
+            'X-Bunq-Include-These-Headers' => ['foo', 'bar'],
+            'Foo' => ['Bar'],
+        ];
+
+        $signatureData = "$statusCode\n";
+        $signatureData .= "X-Bunq-Include-These-Headers: foo\n";
+        $signatureData .= "X-Bunq-Include-These-Headers: bar\n";
+        $signatureData .= "\n$body";
+
+        openssl_sign($signatureData, $signature, TEST_PRIVATE_KEY, OPENSSL_ALGO_SHA256);
+
+        $this->response
+            ->shouldReceive('getHeader')
+            ->withArgs(['X-Bunq-Server-Signature'])
+            ->andReturn([
+                base64_encode($signature)
+        ]);
+
+        $this->response
+            ->shouldReceive('getStatusCode')
+            ->andReturn($statusCode);
+
+        $this->response
+            ->shouldReceive('getHeaders')
+            ->andReturn($headers);
+
+        $this->response
+            ->shouldReceive('getBody')
+            ->andReturn($body);
+
+        $response = ($this->middleware)($this->response);
+        $this->assertSame($response, $this->response);
+    }
+}

From eb4618d4c96ce1ff33d6d6d32438d74aefcb62fe Mon Sep 17 00:00:00 2001
From: Dennis de Greef <github@link0.net>
Date: Sun, 30 Apr 2017 01:12:17 +0200
Subject: [PATCH 2/4] Add test for Id

---
 src/Domain/Id.php            |  7 ++++++-
 tests/unit/Domain/IdTest.php | 35 +++++++++++++++++++++++++++++++++++
 2 files changed, 41 insertions(+), 1 deletion(-)
 create mode 100644 tests/unit/Domain/IdTest.php

diff --git a/src/Domain/Id.php b/src/Domain/Id.php
index e219b81..244f30b 100644
--- a/src/Domain/Id.php
+++ b/src/Domain/Id.php
@@ -29,11 +29,16 @@ public static function fromInteger(int $id): Id
         return new Id($id);
     }
 
+    public function id()
+    {
+        return $this->id;
+    }
+
     /**
      * @return string
      */
     public function __toString()
     {
-        return (string) $this->id;
+        return (string) $this->id();
     }
 }
diff --git a/tests/unit/Domain/IdTest.php b/tests/unit/Domain/IdTest.php
new file mode 100644
index 0000000..e4d6420
--- /dev/null
+++ b/tests/unit/Domain/IdTest.php
@@ -0,0 +1,35 @@
+<?php
+
+namespace Link0\Bunq\Tests\Domain;
+
+use Link0\Bunq\Domain\Id;
+use PHPUnit\Framework\TestCase;
+
+final class IdTest extends TestCase
+{
+    /**
+     * @expectedException \Assert\InvalidArgumentException
+     * @expectedExceptionMessage Id must be greater or equal to 0
+     */
+    public function test_that_id_must_not_be_negative()
+    {
+        Id::fromInteger(-42);
+    }
+
+    public function test_that_id_can_be_zero()
+    {
+        $id = Id::fromInteger(0);
+        $this->assertSame(0, $id->id());
+    }
+    public function test_that_id_can_greater_than_zero()
+    {
+        $id = Id::fromInteger(42);
+        $this->assertSame(42, $id->id());
+    }
+
+    public function test_that_id_can_be_casted_to_string()
+    {
+        $id = Id::fromInteger(42);
+        $this->assertEquals('42', (string) $id);
+    }
+}

From c3bba637460f98aefdab755acc4e400a88721b42 Mon Sep 17 00:00:00 2001
From: Dennis de Greef <github@link0.net>
Date: Sun, 30 Apr 2017 01:12:31 +0200
Subject: [PATCH 3/4] Remove unused import

---
 src/Middleware/DebugMiddleware.php | 1 -
 1 file changed, 1 deletion(-)

diff --git a/src/Middleware/DebugMiddleware.php b/src/Middleware/DebugMiddleware.php
index 509ce00..2942f37 100644
--- a/src/Middleware/DebugMiddleware.php
+++ b/src/Middleware/DebugMiddleware.php
@@ -3,7 +3,6 @@
 namespace Link0\Bunq\Middleware;
 
 use GuzzleHttp\Middleware;
-use GuzzleHttp\Promise\FulfilledPromise;
 use GuzzleHttp\Promise\PromiseInterface;
 use Psr\Http\Message\RequestInterface;
 use Psr\Http\Message\ResponseInterface;

From 035fa6098cb4c2ccfa3df1dbf757bad66da3ec73 Mon Sep 17 00:00:00 2001
From: Dennis de Greef <github@link0.net>
Date: Sun, 30 Apr 2017 23:53:14 +0200
Subject: [PATCH 4/4] Add UserService test

---
 src/Client.php                         |  2 +-
 src/ClientInterface.php                | 35 +++++++++++++++++++
 src/Service/UserService.php            |  7 ++--
 tests/unit/Service/UserServiceTest.php | 48 ++++++++++++++++++++++++++
 4 files changed, 88 insertions(+), 4 deletions(-)
 create mode 100644 src/ClientInterface.php
 create mode 100644 tests/unit/Service/UserServiceTest.php

diff --git a/src/Client.php b/src/Client.php
index 9db12b4..dd3e36e 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -21,7 +21,7 @@
 use Link0\Bunq\Middleware\ResponseSignatureMiddleware;
 use Psr\Http\Message\ResponseInterface;
 
-final class Client
+final class Client implements ClientInterface
 {
     /**
      * @var GuzzleClient
diff --git a/src/ClientInterface.php b/src/ClientInterface.php
new file mode 100644
index 0000000..ff40a8d
--- /dev/null
+++ b/src/ClientInterface.php
@@ -0,0 +1,35 @@
+<?php declare(strict_types=1);
+
+namespace Link0\Bunq;
+
+interface ClientInterface
+{
+    /**
+     * @param string $endpoint
+     * @return array
+     */
+    public function get(string $endpoint, array $headers = []): array;
+
+    /**
+     * @param string $endpoint
+     * @param array $body
+     * @param array $headers
+     * @return array
+     */
+    public function post(string $endpoint, array $body, array $headers = []): array;
+
+    /**
+     * @param string $endpoint
+     * @param array $body
+     * @param array $headers
+     * @return array
+     */
+    public function put(string $endpoint, array $body, array $headers = []): array;
+
+    /**
+     * @param string $endpoint
+     * @param array $headers
+     * @return void
+     */
+    public function delete(string $endpoint, array $headers = []);
+}
diff --git a/src/Service/UserService.php b/src/Service/UserService.php
index f9bf179..a0dfedd 100644
--- a/src/Service/UserService.php
+++ b/src/Service/UserService.php
@@ -3,20 +3,21 @@
 namespace Link0\Bunq\Service;
 
 use Link0\Bunq\Client;
+use Link0\Bunq\ClientInterface;
 use Link0\Bunq\Domain\Id;
 use Link0\Bunq\Domain\User;
 
 final class UserService
 {
     /**
-     * @var Client
+     * @var ClientInterface
      */
     private $client;
 
     /**
-     * @param Client $client
+     * @param ClientInterface $client
      */
-    public function __construct(Client $client)
+    public function __construct(ClientInterface $client)
     {
         $this->client = $client;
     }
diff --git a/tests/unit/Service/UserServiceTest.php b/tests/unit/Service/UserServiceTest.php
new file mode 100644
index 0000000..334753d
--- /dev/null
+++ b/tests/unit/Service/UserServiceTest.php
@@ -0,0 +1,48 @@
+<?php declare(strict_types=1);
+
+namespace Link0\Bunq\Tests\Middleware;
+
+use Link0\Bunq\Client;
+use Link0\Bunq\ClientInterface;
+use Link0\Bunq\Domain\Id;
+use Link0\Bunq\Domain\UserPerson;
+use Link0\Bunq\Service\UserService;
+use Mockery;
+use Mockery\MockInterface;
+use PHPUnit\Framework\TestCase;
+
+final class UserServiceTest extends TestCase
+{
+    /**
+     * @var Client|MockInterface
+     */
+    private $client;
+
+    /**
+     * @var UserService
+     */
+    private $service;
+
+    public function setUp()
+    {
+        $this->client = Mockery::mock(ClientInterface::class);
+        $this->service = new UserService($this->client);
+    }
+
+    public function test_that_list_users_calls_client()
+    {
+        $users = [];
+        $this->client->shouldReceive('get')->withArgs(['user'])->andReturn($users);
+        $actualUsers = $this->service->listUsers();
+        $this->assertSame($users, $actualUsers);
+    }
+
+    public function test_that_user_fetchable_by_id()
+    {
+        $userId = Id::fromInteger(42);
+        $user = null;
+        $this->client->shouldReceive('get')->withArgs(['user/' . $userId])->andReturn($user);
+        $actualUser = $this->service->userById($userId);
+        $this->assertSame($user, $actualUser);
+    }
+}