diff --git a/src/Module/Api/ApiResponse.php b/src/Module/Api/ApiResponse.php
index d0d03da994..c0ce7c756b 100644
--- a/src/Module/Api/ApiResponse.php
+++ b/src/Module/Api/ApiResponse.php
@@ -202,11 +202,9 @@ class ApiResponse
 				break;
 			case 'rss':
 				$this->setHeader('Content-Type: application/rss+xml');
-				$return = '<?xml version="1.0" encoding="UTF-8"?>' . "\n" . $return;
 				break;
 			case 'atom':
 				$this->setHeader('Content-Type: application/atom+xml');
-				$return = '<?xml version="1.0" encoding="UTF-8"?>' . "\n" . $return;
 				break;
 		}
 
diff --git a/tests/legacy/ApiTest.php b/tests/legacy/ApiTest.php
index 9bcf2e1164..73ea1b3327 100644
--- a/tests/legacy/ApiTest.php
+++ b/tests/legacy/ApiTest.php
@@ -622,30 +622,6 @@ class ApiTest extends FixtureTest
 		);
 	}
 
-	/**
-	 * Test the api_call() function with an unallowed method.
-	 *
-	 * @runInSeparateProcess
-	 * @preserveGlobalState disabled
-	 */
-	public function testApiCallWithWrongMethod()
-	{
-		// Shouldn't be needed anymore due to the router?
-		/*
-		global $API;
-		$API['api_path'] = ['method' => 'method'];
-
-		$_SERVER['QUERY_STRING'] = 'pagename=api_path';
-
-		$args = DI::args()->determine($_SERVER, $_GET);
-
-		self::assertEquals(
-			'{"status":{"error":"Method Not Allowed","code":"405 Method Not Allowed","request":"api_path"}}',
-			api_call($this->app, $args)
-		);
-		*/
-	}
-
 	/**
 	 * Test the api_call() function with an unauthorized user.
 	 *
@@ -674,92 +650,6 @@ class ApiTest extends FixtureTest
 		*/
 	}
 
-	/**
-	 * Test the api_error() function with a JSON result.
-	 *
-	 * @runInSeparateProcess
-	 * @preserveGlobalState disabled
-	 */
-	public function testApiErrorWithJson()
-	{
-		// @todo How to test the new API?
-		// self::assertEquals(
-		// 	'{"status":{"error":"error_message","code":"200 OK","request":""}}',
-		// 	api_error('json', new HTTPException\OKException('error_message'), DI::args())
-		// );
-	}
-
-	/**
-	 * Test the api_error() function with an XML result.
-	 *
-	 * @runInSeparateProcess
-	 * @preserveGlobalState disabled
-	 */
-	public function testApiErrorWithXml()
-	{
-		// @todo How to test the new API?
-		/*
-		self::assertEquals(
-			'<?xml version="1.0"?>' . "\n" .
-			'<status xmlns="http://api.twitter.com" xmlns:statusnet="http://status.net/schema/api/1/" ' .
-			'xmlns:friendica="http://friendi.ca/schema/api/1/" ' .
-			'xmlns:georss="http://www.georss.org/georss">' . "\n" .
-			'  <error>error_message</error>' . "\n" .
-			'  <code>200 OK</code>' . "\n" .
-			'  <request/>' . "\n" .
-			'</status>' . "\n",
-			api_error('xml', new HTTPException\OKException('error_message'), DI::args())
-		);
-		*/
-	}
-
-	/**
-	 * Test the api_error() function with an RSS result.
-	 *
-	 * @runInSeparateProcess
-	 * @preserveGlobalState disabled
-	 */
-	public function testApiErrorWithRss()
-	{
-		// @todo How to test the new API?
-		/*
-		self::assertEquals(
-			'<?xml version="1.0"?>' . "\n" .
-			'<status xmlns="http://api.twitter.com" xmlns:statusnet="http://status.net/schema/api/1/" ' .
-			'xmlns:friendica="http://friendi.ca/schema/api/1/" ' .
-			'xmlns:georss="http://www.georss.org/georss">' . "\n" .
-			'  <error>error_message</error>' . "\n" .
-			'  <code>200 OK</code>' . "\n" .
-			'  <request/>' . "\n" .
-			'</status>' . "\n",
-			api_error('rss', new HTTPException\OKException('error_message'), DI::args())
-		);
-		*/
-	}
-
-	/**
-	 * Test the api_error() function with an Atom result.
-	 *
-	 * @runInSeparateProcess
-	 * @preserveGlobalState disabled
-	 */
-	public function testApiErrorWithAtom()
-	{
-		// @todo How to test the new API?
-		/*
-		self::assertEquals(
-			'<?xml version="1.0"?>' . "\n" .
-			'<status xmlns="http://api.twitter.com" xmlns:statusnet="http://status.net/schema/api/1/" ' .
-			'xmlns:friendica="http://friendi.ca/schema/api/1/" ' .
-			'xmlns:georss="http://www.georss.org/georss">' . "\n" .
-			'  <error>error_message</error>' . "\n" .
-			'  <code>200 OK</code>' . "\n" .
-			'  <request/>' . "\n" .
-			'</status>' . "\n",
-			api_error('atom', new HTTPException\OKException('error_message'), DI::args())
-		);
-		*/
-	}
 
 	/**
 	 * Test the api_rss_extra() function.
diff --git a/tests/src/Module/Api/ApiResponseTest.php b/tests/src/Module/Api/ApiResponseTest.php
new file mode 100644
index 0000000000..7499e9a35c
--- /dev/null
+++ b/tests/src/Module/Api/ApiResponseTest.php
@@ -0,0 +1,93 @@
+<?php
+
+namespace Friendica\Test\src\Module\Api;
+
+use Friendica\App\Arguments;
+use Friendica\Core\L10n;
+use Friendica\Test\MockedTest;
+use Friendica\Test\Util\ApiResponseDouble;
+use Psr\Log\NullLogger;
+
+class ApiResponseTest extends MockedTest
+{
+	protected function tearDown(): void
+	{
+		ApiResponseDouble::reset();
+
+		parent::tearDown();
+	}
+
+	public function testErrorWithJson()
+	{
+		$l10n = \Mockery::mock(L10n::class);
+		$args = \Mockery::mock(Arguments::class);
+		$args->shouldReceive('getQueryString')->andReturn('');
+
+		$response = new ApiResponseDouble($l10n, $args, new NullLogger());
+		$response->error(200, 'OK', 'error_message', 'json');
+
+		self::assertEquals('{"error":"error_message","code":"200 OK","request":""}', ApiResponseDouble::getOutput());
+	}
+
+	public function testErrorWithXml()
+	{
+		$l10n = \Mockery::mock(L10n::class);
+		$args = \Mockery::mock(Arguments::class);
+		$args->shouldReceive('getQueryString')->andReturn('');
+
+		$response = new ApiResponseDouble($l10n, $args, new NullLogger());
+		$response->error(200, 'OK', 'error_message', 'xml');
+
+		self::assertEquals('<?xml version="1.0"?>' . "\n" .
+						   '<status xmlns="http://api.twitter.com" xmlns:statusnet="http://status.net/schema/api/1/" ' .
+						   'xmlns:friendica="http://friendi.ca/schema/api/1/" ' .
+						   'xmlns:georss="http://www.georss.org/georss">' . "\n" .
+						   '  <error>error_message</error>' . "\n" .
+						   '  <code>200 OK</code>' . "\n" .
+						   '  <request/>' . "\n" .
+						   '</status>' . "\n",
+			ApiResponseDouble::getOutput());
+	}
+
+	public function testErrorWithRss()
+	{
+		$l10n = \Mockery::mock(L10n::class);
+		$args = \Mockery::mock(Arguments::class);
+		$args->shouldReceive('getQueryString')->andReturn('');
+
+		$response = new ApiResponseDouble($l10n, $args, new NullLogger());
+		$response->error(200, 'OK', 'error_message', 'rss');
+
+		self::assertEquals(
+			'<?xml version="1.0"?>' . "\n" .
+			'<status xmlns="http://api.twitter.com" xmlns:statusnet="http://status.net/schema/api/1/" ' .
+			'xmlns:friendica="http://friendi.ca/schema/api/1/" ' .
+			'xmlns:georss="http://www.georss.org/georss">' . "\n" .
+			'  <error>error_message</error>' . "\n" .
+			'  <code>200 OK</code>' . "\n" .
+			'  <request/>' . "\n" .
+			'</status>' . "\n",
+			ApiResponseDouble::getOutput());
+	}
+
+	public function testErrorWithAtom()
+	{
+		$l10n = \Mockery::mock(L10n::class);
+		$args = \Mockery::mock(Arguments::class);
+		$args->shouldReceive('getQueryString')->andReturn('');
+
+		$response = new ApiResponseDouble($l10n, $args, new NullLogger());
+		$response->error(200, 'OK', 'error_message', 'atom');
+
+		self::assertEquals(
+			'<?xml version="1.0"?>' . "\n" .
+			'<status xmlns="http://api.twitter.com" xmlns:statusnet="http://status.net/schema/api/1/" ' .
+			'xmlns:friendica="http://friendi.ca/schema/api/1/" ' .
+			'xmlns:georss="http://www.georss.org/georss">' . "\n" .
+			'  <error>error_message</error>' . "\n" .
+			'  <code>200 OK</code>' . "\n" .
+			'  <request/>' . "\n" .
+			'</status>' . "\n",
+			ApiResponseDouble::getOutput());
+	}
+}