diff --git a/tests/phpunit/tests/comment/isAvatarCommentType.php b/tests/phpunit/tests/comment/isAvatarCommentType.php
new file mode 100644
index 0000000000..9e0111cc04
--- /dev/null
+++ b/tests/phpunit/tests/comment/isAvatarCommentType.php
@@ -0,0 +1,81 @@
+<?php
+/**
+ * Test cases for the `is_avatar_comment_type()` function.
+ *
+ * @package WordPress\UnitTests
+ *
+ * @since 5.1.0
+ */
+
+/**
+ * Tests_Comment_IsAvatarCommentType class.
+ *
+ * @group comment
+ * @covers is_avatar_comment_type
+ *
+ * @since 5.1.0
+ */
+class Tests_Comment_IsAvatarCommentType extends WP_UnitTestCase {
+	/**
+	 * Test the `is_avatar_comment_type()` function.
+	 *
+	 * @since 5.1.0
+	 *
+	 * @dataProvider data_is_avatar_comment_type
+	 */
+	public function test_function( $comment_type, $expected ) {
+		$this->assertSame( $expected, is_avatar_comment_type( $comment_type ) );
+	}
+
+	/**
+	 * Dataprovider for `is_avatar_comment_type()`.
+	 *
+	 * @since 5.1.0
+	 *
+	 * @return array {
+	 *     @type array {
+	 *         @type string Comment type.
+	 *         @type bool   Expected values.
+	 *     }
+	 * }
+	 */
+	public function data_is_avatar_comment_type() {
+		return array(
+			array( null, false ),
+			array( '', false ),
+			array( 'non-existing-comment-type', false ),
+			array( 'comment', true ),
+		);
+	}
+
+	/**
+	 * The function should be filterable with the `get_avatar_comment_types` filter.
+	 *
+	 * @since 5.1.0
+	 */
+	public function test_function_should_be_filterable() {
+		$this->assertFalse( is_avatar_comment_type( 'review' ) );
+
+		add_filter( 'get_avatar_comment_types', array( $this, '_filter_avatar_comment_types' ) );
+		$actual_comment = is_avatar_comment_type( 'comment' );
+		$actual_review  = is_avatar_comment_type( 'review' );
+		remove_filter( 'get_avatar_comment_types', array( $this, '_filter_avatar_comment_types' ) );
+
+		$this->assertTrue( $actual_comment );
+		$this->assertTrue( $actual_review );
+	}
+
+	/**
+	 * Filters callback that modifies the list of allowed comment types for retrieving avatars.
+	 *
+	 * @since 5.1.0
+	 *
+	 * @param  array $types An array of content types.
+	 * @return array $types An array of content types.
+	 */
+	public function _filter_avatar_comment_types( $types ) {
+		$types[] = 'review';
+		return $types;
+	}
+
+}