ICursorTest: added test for fetchOneAt(<negative>)

tests/Store/PostgresDriver/ICursorTest.php

@@ -218,6 +218,14 @@ abstract class ICursorTest extends BaseTest
 		Assert::same(5, $data["n"]);
 	}
 
+	public function test_givenInitialPosition_whenFetchMinus2_thenGetSecondFromRight()
+	{
+		$this->uut->moveTo(234); // wherever
+
+		$data = $this->uut->fetchOneAt(-2);
+		Assert::same(999, $data["n"]);
+	}
+
 
 	// fetchOneBy()
 	public function test_givenInitialPosition_whenFetchCurrent_thenGetNull()