What means E letter in phpunit tests?

What means letters E and F in PHPUnit tests?

..............F................................................  63 / 348 ( 18%)
.............................................................F. 126 / 348 ( 36%)
............................................................... 189 / 348 ( 54%)
.........E..................................................... 252 / 348 ( 72%)
...................................................F........... 315 / 348 ( 90%)
.................................                               348 / 348 (100%)