You can install following official guide: Installation Guide or following unofficial guide.

Linux installation guide

Step 01: check your enviroment

$ python
Python 2.7.5 (default, Oct 30 2018, 23:45:53) 
[GCC 4.8.5 20150623 (Red Hat 4.8.5-36)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import gtk
>>>

make sure you already have PyGTK installed.

Step 02: install texttest

$ git clone git@github.com:scutse/texttest.git
$ cd texttest
$ python setup.py install

Step03: use texttest

$ texttest

and you can get the following window:

That you done!