diff --git a/phpBB/language/en/common.php b/phpBB/language/en/common.php
index 79128293e2..25851d738e 100644
--- a/phpBB/language/en/common.php
+++ b/phpBB/language/en/common.php
@@ -525,6 +525,7 @@ $lang = array_merge($lang, array(
 	'NO_EMAIL_SUBJECT'			=> 'No email subject specified.',
 	'NO_FORUM'					=> 'The forum you selected does not exist.',
 	'NO_FORUMS'					=> 'This board has no forums.',
+	'NO_GENERATOR_CLASS'		=> 'No generator class given.',
 	'NO_GROUP'					=> 'The requested usergroup does not exist.',
 	'NO_GROUP_MEMBERS'			=> 'This group currently has no members.',
 	'NO_IPS_DEFINED'			=> 'No IP addresses or hostnames defined',
diff --git a/phpBB/phpbb/captcha/plugins/incomplete.php b/phpBB/phpbb/captcha/plugins/incomplete.php
index 5c2b7f9a66..37301c45f5 100644
--- a/phpBB/phpbb/captcha/plugins/incomplete.php
+++ b/phpBB/phpbb/captcha/plugins/incomplete.php
@@ -14,6 +14,7 @@
 namespace phpbb\captcha\plugins;
 
 use phpbb\config\config;
+use phpbb\exception\runtime_exception;
 use phpbb\template\template;
 
 class incomplete extends captcha_abstract
@@ -39,12 +40,14 @@ class incomplete extends captcha_abstract
 	}
 
 	/**
-	 * Dummy implementation
+	 * Dummy implementation, not supported by this captcha
 	 *
+	 * @throws runtime_exception
 	 * @return void
 	 */
-	public function get_generator_class()
+	public function get_generator_class(): void
 	{
+		throw new runtime_exception('NO_GENERATOR_CLASS');
 	}
 
 	/**
@@ -65,6 +68,7 @@ class incomplete extends captcha_abstract
 	 */
 	public function init($type)
 	{
+		$this->type = (int) $type;
 	}
 
 	/**
diff --git a/phpBB/phpbb/captcha/plugins/recaptcha.php b/phpBB/phpbb/captcha/plugins/recaptcha.php
index 399eb34b6b..ef30baaa9b 100644
--- a/phpBB/phpbb/captcha/plugins/recaptcha.php
+++ b/phpBB/phpbb/captcha/plugins/recaptcha.php
@@ -13,6 +13,8 @@
 
 namespace phpbb\captcha\plugins;
 
+use phpbb\exception\runtime_exception;
+
 class recaptcha extends captcha_abstract
 {
 	private $response;
@@ -55,10 +57,11 @@ class recaptcha extends captcha_abstract
 
 	/**
 	* This function is implemented because required by the upper class, but is never used for reCaptcha.
+	* @throws runtime_exception
 	*/
 	function get_generator_class()
 	{
-		throw new \Exception('No generator class given.');
+		throw new runtime_exception('NO_GENERATOR_CLASS');
 	}
 
 	function acp_page($id, $module)
diff --git a/phpBB/phpbb/captcha/plugins/recaptcha_v3.php b/phpBB/phpbb/captcha/plugins/recaptcha_v3.php
index 02dacb4b51..67035ab1c6 100644
--- a/phpBB/phpbb/captcha/plugins/recaptcha_v3.php
+++ b/phpBB/phpbb/captcha/plugins/recaptcha_v3.php
@@ -13,6 +13,8 @@
 
 namespace phpbb\captcha\plugins;
 
+use phpbb\exception\runtime_exception;
+
 /**
  * Google reCAPTCHA v3 plugin.
  */
@@ -86,12 +88,12 @@ class recaptcha_v3 extends captcha_abstract
 	 *
 	 * Not needed by this CAPTCHA plugin.
 	 *
-	 * @throws \Exception
+	 * @throws runtime_exception
 	 * @return void
 	 */
 	public function get_generator_class()
 	{
-		throw new \Exception('No generator class given.');
+		throw new runtime_exception('NO_GENERATOR_CLASS');
 	}
 
 	/**
diff --git a/tests/captcha/incomplete_test.php b/tests/captcha/incomplete_test.php
new file mode 100644
index 0000000000..88b6825fa9
--- /dev/null
+++ b/tests/captcha/incomplete_test.php
@@ -0,0 +1,86 @@
+<?php
+/**
+ *
+ * This file is part of the phpBB Forum Software package.
+ *
+ * @copyright (c) phpBB Limited <https://www.phpbb.com>
+ * @license GNU General Public License, version 2 (GPL-2.0)
+ *
+ * For full copyright and license information, please see
+ * the docs/CREDITS.txt file.
+ *
+ */
+
+use phpbb\captcha\plugins\incomplete;
+use phpbb\config\config;
+use phpbb\template\template;
+
+class phpbb_captcha_incomplete_test extends phpbb_test_case
+{
+	protected config $config;
+
+	protected template $template;
+
+
+	/** @var incomplete */
+	protected incomplete $incomplete_captcha;
+
+	protected array $assigned_vars = [];
+
+	public function assign_vars(array $vars): void
+	{
+		$this->assigned_vars = array_merge($this->assigned_vars, $vars);
+	}
+
+	protected function setUp(): void
+	{
+		global $phpbb_root_path, $phpEx;
+
+		$this->config = new config([]);
+		$this->template = $this->getMockBuilder('\phpbb\template\twig\twig')
+			->setMethods(['assign_vars'])
+			->disableOriginalConstructor()
+			->getMock();
+		$this->template->method('assign_vars')
+			->willReturnCallback([$this, 'assign_vars']);
+
+		$this->incomplete_captcha = new incomplete(
+			$this->config,
+			$this->template,
+			$phpbb_root_path,
+			$phpEx
+		);
+	}
+
+	public function test_miscellaneous_incomplete(): void
+	{
+		$this->assertTrue($this->incomplete_captcha->is_available());
+		$this->assertFalse($this->incomplete_captcha->is_solved());
+		$this->assertFalse($this->incomplete_captcha->validate());
+		$this->assertSame('CAPTCHA_INCOMPLETE', incomplete::get_name());
+		$this->incomplete_captcha->init(0);
+		$this->incomplete_captcha->execute();
+		$this->incomplete_captcha->execute_demo();
+		$this->assertEmpty($this->assigned_vars);
+		$this->assertEmpty($this->incomplete_captcha->get_demo_template(0));
+	}
+
+	public function test_get_generator_class(): void
+	{
+		$this->expectException(\phpbb\exception\runtime_exception::class);
+		$this->incomplete_captcha->get_generator_class();
+	}
+
+	public function test_get_tempate(): void
+	{
+		$this->incomplete_captcha->init(CONFIRM_REG);
+		$this->assertSame('captcha_incomplete.html', $this->incomplete_captcha->get_template());
+		$this->assertEquals('CONFIRM_INCOMPLETE', $this->assigned_vars['CONFIRM_LANG']);
+
+		$this->assigned_vars = [];
+
+		$this->incomplete_captcha->init(CONFIRM_POST);
+		$this->assertSame('captcha_incomplete.html', $this->incomplete_captcha->get_template());
+		$this->assertEquals('POST_CONFIRM_INCOMPLETE', $this->assigned_vars['CONFIRM_LANG']);
+	}
+}