tests: replace all "assert" by unittest assertions

If the assert fails because of a comparison, it is useful that the
test suite log contains a comparison of these values.
unittest.assertEqual() and friends do that for us.

* HACKING: Add a section about Python tests.
* tests/sanity/style.test: Forbid the use of "assert" in
Python tests.
* tests/python/298.py, tests/python/341.py, tests/python/471.py,
tests/python/accparse2.py, tests/python/aiger.py,
tests/python/aliases.py, tests/python/alternating.py,
tests/python/bdddict.py, tests/python/bdditer.py,
tests/python/bugdet.py, tests/python/complement_semidet.py,
tests/python/declenv.py, tests/python/decompose_scc.py,
tests/python/det.py, tests/python/dualize.py, tests/python/ecfalse.py,
tests/python/except.py, tests/python/game.py, tests/python/gen.py,
tests/python/genem.py, tests/python/implies.py,
tests/python/intrun.py, tests/python/kripke.py,
tests/python/langmap.py, tests/python/ltl2tgba.py,
tests/python/ltlf.py, tests/python/ltlparse.py,
tests/python/ltlsimple.py, tests/python/mealy.py,
tests/python/merge.py, tests/python/mergedge.py,
tests/python/misc-ec.py, tests/python/optionmap.py,
tests/python/origstate.py, tests/python/otfcrash.py,
tests/python/parity.py, tests/python/parsetgba.py,
tests/python/pdegen.py, tests/python/prodexpt.py,
tests/python/randgen.py, tests/python/relabel.py,
tests/python/remfin.py, tests/python/removeap.py,
tests/python/rs_like.py, tests/python/satmin.py,
tests/python/sbacc.py, tests/python/sccfilter.py,
tests/python/sccinfo.py, tests/python/sccsplit.py,
tests/python/semidet.py, tests/python/setacc.py,
tests/python/setxor.py, tests/python/simplacc.py,
tests/python/simstate.py, tests/python/sonf.py, tests/python/split.py,
tests/python/streett_totgba.py, tests/python/streett_totgba2.py,
tests/python/stutter.py, tests/python/sum.py,
tests/python/synthesis.py, tests/python/toparity.py,
tests/python/toweak.py, tests/python/tra2tba.py,
tests/python/trival.py, tests/python/twagraph.py,
tests/python/zlktree.py: Replace all occurrences of "assert" by calls
to unittest.TestCase methods.

tests/python/streett_totgba.py

@@ -1,7 +1,7 @@
 #!/usr/bin/python3
 # -*- mode: python; coding: utf-8 -*-
-# Copyright (C) 2017, 2018, 2021 Laboratoire de Recherche et Développement de
-# l'EPITA.
+# Copyright (C) 2017-2018, 2021-2022 Laboratoire de Recherche et
+# Développement de l'EPITA.
 #
 # This file is part of Spot, a model checking library.
 #
@@ -22,7 +22,8 @@ import spot
 import os
 import shutil
 import sys
-
+from unittest import TestCase
+tc = TestCase()
 
 def tgba(a):
     if not a.is_existential():
@@ -33,11 +34,11 @@ def tgba(a):
 
 def test_aut(aut):
     stgba = tgba(aut)
-    assert stgba.equivalent_to(aut)
+    tc.assertTrue(stgba.equivalent_to(aut))
     os.environ["SPOT_STREETT_CONV_MIN"] = '1'
     sftgba = tgba(aut)
     del os.environ["SPOT_STREETT_CONV_MIN"]
-    assert stgba.equivalent_to(sftgba)
+    tc.assertTrue(stgba.equivalent_to(sftgba))
 
     slike = spot.simplify_acceptance(aut)
 
@@ -45,8 +46,7 @@ def test_aut(aut):
     os.environ["SPOT_STREETT_CONV_MIN"] = "1"
     slftgba = tgba(slike)
     del os.environ["SPOT_STREETT_CONV_MIN"]
-    assert sltgba.equivalent_to(slftgba)
-
+    tc.assertTrue(sltgba.equivalent_to(slftgba))
 
 if shutil.which('ltl2dstar') is None:
     sys.exit(77)