@Test
public void testLog_messageOnly() {

    Span result = undertest.log("my message");
    assertSame(result, undertest);
    assertEquals(1, grpcSpan.getLogsCount());
    Log logRecord = grpcSpan.getLogs(0);
    Map<String, String> fieldMap = getLogFieldMap(logRecord);
    assertEquals("my message", fieldMap.get("message"));
    assertNull(fieldMap.get("payload"));
    assertNotNull(logRecord.getTimestamp());
}