diff --git a/tests/phpunit/tests/admin/includes/misc/saveDomDocument.php b/tests/phpunit/tests/admin/includes/misc/saveDomDocument.php
new file mode 100644
index 0000000000000..ccb5038c65951
--- /dev/null
+++ b/tests/phpunit/tests/admin/includes/misc/saveDomDocument.php
@@ -0,0 +1,78 @@
+<?php
+/**
+ * Tests for the saveDomDocument() function.
+ *
+ * @group admin
+ *
+ * @covers ::saveDomDocument
+ */
+class Tests_saveDomDocument extends WP_UnitTestCase {
+	/**
+	 * Path to the temporary file.
+	 *
+	 * @var string
+	 */
+	private $temp_file;
+
+	/**
+	 * Set up the test environment.
+	 */
+	public function set_up() {
+		parent::set_up();
+		require_once ABSPATH . 'wp-admin/includes/misc.php';
+		$this->temp_file = wp_tempnam( 'saveDomDocument' );
+	}
+
+	/**
+	 * Clean up the test environment.
+	 */
+	public function tear_down() {
+		if ( file_exists( $this->temp_file ) ) {
+			unlink( $this->temp_file );
+		}
+		parent::tear_down();
+	}
+
+	/**
+	 * Tests that saveDomDocument() correctly saves a DOMDocument to a file.
+	 *
+	 * @ticket 65173
+	 */
+	public function test_saveDomDocument_saves_file() {
+		$doc  = new DOMDocument();
+		$root = $doc->createElement( 'root' );
+		$doc->appendChild( $root );
+
+		saveDomDocument( $doc, $this->temp_file );
+
+		$this->assertFileExists( $this->temp_file, 'The file should be saved.' );
+		$this->assertXmlStringEqualsXmlFile( $this->temp_file, $doc->saveXML(), 'The saved file content should match the XML.' );
+	}
+
+	/**
+	 * Tests that saveDomDocument() converts LF to CRLF.
+	 *
+	 * @ticket 65173
+	 */
+	public function test_saveDomDocument_converts_line_endings() {
+		$doc = new DOMDocument();
+		// Create a multi-line XML.
+		$root   = $doc->createElement( 'root' );
+		$child1 = $doc->createElement( 'child', 'one' );
+		$child2 = $doc->createElement( 'child', 'two' );
+		$root->appendChild( $child1 );
+		$root->appendChild( $child2 );
+		$doc->appendChild( $root );
+		$doc->formatOutput = true;
+
+		saveDomDocument( $doc, $this->temp_file );
+
+		$content = file_get_contents( $this->temp_file );
+
+		// The function replaces [^\r]\n with \r\n.
+		// Note: DOMDocument::saveXML() usually outputs LF on Linux environments where these tests run in Docker.
+
+		$this->assertStringContainsString( "\r\n", $content, 'The output should contain CRLF line endings.' );
+		$this->assertStringNotContainsString( "(?<!\r)\n", $content, 'The output should not contain bare LF line endings.' );
+	}
+}