Test cases for twisted.logger._format.
| Class | FormattingTests | Tests for basic event formatting functions. | 
| Class | TimeFormattingTests | Tests for time formatting functions. | 
| Class | ClassicLogFormattingTests | Tests for classic text log event formatting functions. | 
| Class | FormatFieldTests | Tests for format field functions. | 
| Class | Unformattable | An object that raises an exception from __repr__. | 
| Class | CapturedError | A captured error for use in format tests. | 
| Class | EventAsTextTests | Tests for eventAsText, all of
which ensure that the returned type is UTF-8 decoded text. |