diff --git a/tests/Behat/Bootstrap/AttachmentContextTrait.php b/tests/Behat/Bootstrap/AttachmentContextTrait.php
index 7b234891..63a86b75 100644
--- a/tests/Behat/Bootstrap/AttachmentContextTrait.php
+++ b/tests/Behat/Bootstrap/AttachmentContextTrait.php
@@ -45,4 +45,18 @@ public function iShowTheAttachmentWithTheId(int $attachmentId)
             $api->getLastResponse()
         );
     }
+
+    /**
+     * @When I download the attachment with the id :attachmentId
+     */
+    public function iDownloadTheAttachmentWithTheId(int $attachmentId)
+    {
+        /** @var Attachment */
+        $api = $this->getNativeCurlClient()->getApi('attachment');
+
+        $this->registerClientResponse(
+            $api->download($attachmentId),
+            $api->getLastResponse()
+        );
+    }
 }
diff --git a/tests/Behat/Bootstrap/FeatureContext.php b/tests/Behat/Bootstrap/FeatureContext.php
index 3a4ac40f..d51a9fa2 100644
--- a/tests/Behat/Bootstrap/FeatureContext.php
+++ b/tests/Behat/Bootstrap/FeatureContext.php
@@ -150,6 +150,14 @@ public function theResponseHasTheContent(string $content)
         $this->assertSame($content, $this->lastResponse->getContent());
     }
 
+    /**
+     * @Then the response has the content
+     */
+    public function theResponseHasTheContentWithMultipleLines(PyStringNode $string)
+    {
+        $this->assertSame($string->getRaw(), $this->lastResponse->getContent());
+    }
+
     /**
      * @Then the returned data is true
      */
@@ -174,6 +182,14 @@ public function theReturnedDataIsExactly(string $content)
         $this->assertSame($content, $this->lastReturn);
     }
 
+    /**
+     * @Then the returned data is exactly
+     */
+    public function theReturnedDataIsExactlyWithMultipleLines(PyStringNode $string)
+    {
+        $this->assertSame($string->getRaw(), $this->lastReturn);
+    }
+
     /**
      * @Then the returned data is an instance of :className
      */
diff --git a/tests/Behat/features/attachments.feature b/tests/Behat/features/attachments.feature
index e68c12da..13c42362 100644
--- a/tests/Behat/features/attachments.feature
+++ b/tests/Behat/features/attachments.feature
@@ -64,3 +64,34 @@ Feature: Interacting with the REST API for attachments
             | property          | value                                                                |
             | id                | 1                                                                    |
             | name              | Redmine Admin                                                        |
+
+    @attachment @error
+    Scenario: Try to show details of a non-existing attachment
+        Given I have a "NativeCurlClient" client
+        When I show the attachment with the id "1"
+        Then the response has the status code "404"
+        And the response has the content type "application/json"
+        And the response has the content ""
+        And the returned data is false
+
+    @attachment
+    Scenario: Downloading an attachment
+        Given I have a "NativeCurlClient" client
+        And I upload the content of the file "%tests_dir%/Fixtures/testfile_01.txt" with the following data
+            | property          | value                |
+            | filename          | testfile.txt         |
+        When I download the attachment with the id "1"
+        Then the response has the status code "200"
+        And the response has the content type "text/plain"
+        And the response has the content
+            """
+            This is a test file.
+            It will be needed for testing file uploads.
+
+            """
+        And the returned data is exactly
+            """
+            This is a test file.
+            It will be needed for testing file uploads.
+
+            """
diff --git a/tests/Unit/Api/Attachment/DownloadTest.php b/tests/Unit/Api/Attachment/DownloadTest.php
new file mode 100644
index 00000000..dc82f636
--- /dev/null
+++ b/tests/Unit/Api/Attachment/DownloadTest.php
@@ -0,0 +1,47 @@
+<?php
+
+namespace Redmine\Tests\Unit\Api\Attachment;
+
+use PHPUnit\Framework\TestCase;
+use Redmine\Api\Attachment;
+use Redmine\Tests\Fixtures\AssertingHttpClient;
+
+/**
+ * @covers \Redmine\Api\Attachment::download
+ */
+class DownloadTest extends TestCase
+{
+    /**
+     * @dataProvider getDownloadData
+     */
+    public function testDownloadReturnsCorrectResponse($id, $expectedPath, $response, $expectedReturn)
+    {
+        $client = AssertingHttpClient::create(
+            $this,
+            [
+                'GET',
+                $expectedPath,
+                '',
+                '',
+                200,
+                'application/json',
+                $response
+            ]
+        );
+
+        // Create the object under test
+        $api = new Attachment($client);
+
+        // Perform the tests
+        $this->assertSame($expectedReturn, $api->download($id));
+    }
+
+    public static function getDownloadData(): array
+    {
+        return [
+            'string response with integer id' => [5, '/attachments/download/5', 'attachment-content', 'attachment-content'],
+            'string response with string id' => ['5', '/attachments/download/5', 'attachment-content', 'attachment-content'],
+            'false response' => [5, '/attachments/download/5', '', false],
+        ];
+    }
+}
diff --git a/tests/Unit/Api/AttachmentTest.php b/tests/Unit/Api/AttachmentTest.php
index efaa5564..d37f2c9e 100644
--- a/tests/Unit/Api/AttachmentTest.php
+++ b/tests/Unit/Api/AttachmentTest.php
@@ -58,34 +58,6 @@ public static function responseCodeProvider(): array
         ];
     }
 
-    /**
-     * Test download().
-     *
-     * @covers ::download
-     * @test
-     */
-    public function testDownloadReturnsUndecodedClientGetResponse()
-    {
-        // Test values
-        $response = 'API Response';
-
-        // Create the used mock objects
-        $client = $this->createMock(Client::class);
-        $client->expects($this->once())
-            ->method('requestGet')
-            ->with($this->equalTo('/attachments/download/5'))
-            ->willReturn(true);
-        $client->expects($this->exactly(1))
-            ->method('getLastResponseBody')
-            ->willReturn($response);
-
-        // Create the object under test
-        $api = new Attachment($client);
-
-        // Perform the tests
-        $this->assertSame($response, $api->download(5));
-    }
-
     /**
      * Test upload().
      *