diff --git a/tests/phpunit/tests/load/timerFloat.php b/tests/phpunit/tests/load/timerFloat.php
new file mode 100644
index 0000000000000..2e684589acc65
--- /dev/null
+++ b/tests/phpunit/tests/load/timerFloat.php
@@ -0,0 +1,60 @@
+<?php
+
+/**
+ * Tests for timer_float().
+ *
+ * @group load
+ *
+ * @covers ::timer_float
+ */
+class Tests_Load_TimerFloat extends WP_UnitTestCase {
+
+	/**
+	 * Original $_SERVER['REQUEST_TIME_FLOAT'] value.
+	 *
+	 * @var float|null
+	 */
+	private $original_request_time_float;
+
+	public function set_up() {
+		parent::set_up();
+
+		$this->original_request_time_float = $_SERVER['REQUEST_TIME_FLOAT'] ?? null;
+	}
+
+	public function tear_down() {
+		if ( null !== $this->original_request_time_float ) {
+			$_SERVER['REQUEST_TIME_FLOAT'] = $this->original_request_time_float;
+		} else {
+			unset( $_SERVER['REQUEST_TIME_FLOAT'] );
+		}
+
+		parent::tear_down();
+	}
+
+	/**
+	 * @ticket 65819
+	 */
+	public function test_returns_elapsed_seconds_as_float() {
+		$_SERVER['REQUEST_TIME_FLOAT'] = microtime( true ) - 1.25;
+
+		$result = timer_float();
+
+		$this->assertIsFloat( $result );
+		$this->assertGreaterThanOrEqual( 1.25, $result );
+		$this->assertLessThanOrEqual( microtime( true ) - $_SERVER['REQUEST_TIME_FLOAT'], $result );
+	}
+
+	/**
+	 * @ticket 65819
+	 */
+	public function test_elapsed_time_increases() {
+		$_SERVER['REQUEST_TIME_FLOAT'] = microtime( true );
+
+		$first = timer_float();
+		usleep( 10000 ); // 10ms.
+		$second = timer_float();
+
+		$this->assertGreaterThan( $first, $second );
+	}
+}