How to compare two files as part of unittest, while getting useful output in case of mismatch?

Question

As part of some Python tests using the unittest framework, I need to compare two relatively short text files, where the one is a test output file and the other is a reference file.

The immediate approach is:

import filecmp ... self.assertTrue(filecmp.cmp(tst_path, ref_path, shallow=False)) 

It works fine if the test passes, but in the even of failure, there is not much help in the output:

AssertionError: False is not true

Is there a better way of comparing two files as part of the unittest framework, so some useful output is generated in case of mismatch?

Answer 1

To get a report of which line has a difference, and a printout of that line, use assertListEqual on the contents, e.g

import io  self.assertListEqual(     list(io.open(tst_path)),     list(io.open(ref_path)))