diff --git a/tests/phpunit/tests/functions.php b/tests/phpunit/tests/functions.php
index ea7488a5d9..7f855e110f 100644
--- a/tests/phpunit/tests/functions.php
+++ b/tests/phpunit/tests/functions.php
@@ -2065,41 +2065,6 @@ class Tests_Functions extends WP_UnitTestCase {
 		$this->assertFalse( wp_get_default_extension_for_mime_type( null ), 'false not returned when null as mime type supplied' );
 	}
 
-	/**
-	 * @ticket 49412
-	 * @covers ::wp_filesize
-	 */
-	function test_wp_filesize_with_nonexistent_file() {
-		$file = 'nonexistent/file.jpg';
-		$this->assertSame( 0, wp_filesize( $file ) );
-	}
-
-	/**
-	 * @ticket 49412
-	 * @covers ::wp_filesize
-	 */
-	function test_wp_filesize() {
-		$file = DIR_TESTDATA . '/images/test-image-upside-down.jpg';
-
-		$this->assertSame( filesize( $file ), wp_filesize( $file ) );
-
-		$filter = function() {
-			return 999;
-		};
-
-		add_filter( 'wp_filesize', $filter );
-
-		$this->assertSame( 999, wp_filesize( $file ) );
-
-		$pre_filter = function() {
-			return 111;
-		};
-
-		add_filter( 'pre_wp_filesize', $pre_filter );
-
-		$this->assertSame( 111, wp_filesize( $file ) );
-	}
-
 	/**
 	 * @ticket 55505
 	 * @covers ::wp_recursive_ksort
diff --git a/tests/phpunit/tests/functions/wpFilesize.php b/tests/phpunit/tests/functions/wpFilesize.php
new file mode 100644
index 0000000000..f65aa90872
--- /dev/null
+++ b/tests/phpunit/tests/functions/wpFilesize.php
@@ -0,0 +1,53 @@
+<?php
+
+/**
+ * Tests for the wp_filesize() function.
+ *
+ * @group functions.php
+ * @covers ::wp_filesize
+ */
+class Tests_Functions_wpFilesize extends WP_UnitTestCase {
+
+	/**
+	 * @ticket 49412
+	 */
+	function test_wp_filesize() {
+		$file = DIR_TESTDATA . '/images/test-image-upside-down.jpg';
+
+		$this->assertSame( filesize( $file ), wp_filesize( $file ) );
+	}
+
+	/**
+	 * @ticket 49412
+	 */
+	function test_wp_filesize_filters() {
+		$file = DIR_TESTDATA . '/images/test-image-upside-down.jpg';
+
+		add_filter(
+			'wp_filesize',
+			static function() {
+				return 999;
+			}
+		);
+
+		$this->assertSame( 999, wp_filesize( $file ) );
+
+		add_filter(
+			'pre_wp_filesize',
+			static function() {
+				return 111;
+			}
+		);
+
+		$this->assertSame( 111, wp_filesize( $file ) );
+	}
+
+	/**
+	 * @ticket 49412
+	 */
+	function test_wp_filesize_with_nonexistent_file() {
+		$file = 'nonexistent/file.jpg';
+
+		$this->assertSame( 0, wp_filesize( $file ) );
+	}
+}