verify(mockCtx, atLeastOnce()).getConfig(); // interaction with dependency
    }

    @Test
    @DisplayName("openConnection with null URL throws NullPointerException")
    void testOpenConnection_NullInput() {
        // Arrange
        Handler handler = newHandlerWith(mockCtx);

        // Act & Assert
        assertThrows(NullPointerException.class, () -> handler.openConnection(null), "Null URL should throw NPE");