assertTrue(str.contains("filename=testfile.txt"), "toString must contain the supplied filename");
    }

    @Test
    @DisplayName("writeBytesWireFormat with null path returns minimal bytes")
    void testWriteWhenPathIsNull() {
        // When path is null, Strings.getOEMBytes returns empty array, not NPE
        when(mockConfig.getOemEncoding()).thenReturn("windows-1252");