Fix #6 use sha1 instead of hash function result

Problem
-------
Plug-in fails to read value from .previous file as its format has changed.
In the version before 0.2.1 the file contained requirements file copy. Now it
keeps integer value, result of 'hash' function on serialized set of parsed
requirements.

Solution
--------
Use SHA1 to describe unique set of the requirements. This function is more
reliable than Python 'hash' function. 'hash' function may produce different
values for the same input as it depends on a seed or depends on PYTHONHASHSEED
value.
Side-effect of using SHA1 that even if file is in the old format it will be just
rewritten with a new hash value and environment is rebuilt.

Testing
-------
Updated existing test-case to ensure that SHA1 is saved in the .previous file.

Makefile

@@ -2,7 +2,7 @@ run-tests:
 	tox -- py.test --pep8 tests
 
 run-tests-continuously:
-	tox -e py35 -- py.test -vv --pep8 --looponfail tests
+	tox -e py35 -- py.test --last-failed -vv --pep8 --looponfail tests
 
 upload-to-pypi:
 	python setup.py sdist bdist_wheel upload

setup.py

@@ -11,7 +11,7 @@ def content_of(fpath):
     description='Additional functionality for tox',
     long_description=content_of("README.rst"),
     license='http://opensource.org/licenses/MIT',
-    version='0.3',
+    version='0.4',
     author='Volodymyr Vitvitskyi',
     author_email='contact.volodymyr@gmail.com',
     url='https://github.com/signalpillar/tox-battery',

tests/test_requirements.py

@@ -50,12 +50,12 @@ def test_venv_recreated_with_simple_changes_in_file(tmpdir):
         textwrap.dedent('''
         pep8
         pytest-xdist==1.13.0
+        # ^ dependency for testing
     '''))
     run('tox -e python -- python -V'.split(), tmpdir)
 
     # verify
     assert not os.path.isfile(marker_fpath)
-    # assert True
 
 
 def test_venv_notrecreated_without_requirements_file_update(tmpdir):
@@ -76,7 +76,7 @@ def test_venv_notrecreated_without_requirements_file_update(tmpdir):
         [tox]
         skipsdist=True
 
-        [testenv:python]
+        [testenv:testenvname]
         deps = -rreq1/requirements.txt
         commands = {posargs}
     '''))
@@ -86,15 +86,20 @@ def test_venv_notrecreated_without_requirements_file_update(tmpdir):
         pytest-xdist==1.13.0
         pep8
     '''))
-    run('tox -e python -- python -V'.split(), tmpdir)
+    run('tox -e testenvname -- python -V'.split(), tmpdir)
     marker_fpath = path('.tox/python/marker.file')
     update_file(marker_fpath, '')
 
     # excercise
     # nothing chnaged in the file
-    run('tox -e python -- python -V'.split(), tmpdir)
+    run('tox -e testenvname -- python -V'.split(), tmpdir)
 
-    # verify that marker file exists as we didn't recreate environment
+    # verify
+    previous_state_hash_file = path('.tox/req1-requirements.txt.testenvname.previous')
+    # Ensure file with current requirements saved as a hash.
+    assert os.path.isfile(previous_state_hash_file)
+    assert read_text_file(previous_state_hash_file) == 'fe75072a8b7548c8ef6a18ecfae1506c16c90ba3'
+    # Verify that marker file exists as we didn't recreate environment.
     assert os.path.isfile(marker_fpath)
 
 
@@ -154,7 +159,8 @@ def test_venv_recreated_on_nested_requirements_file_update(tmpdir):
 
 
 def test_venv_not_recreated_when_nested_requirements_file_do_not_change(tmpdir):
-    """Ensures the venvs do not get recreated when nothing changes in the nested rquirements files."""
+    """Ensures the venvs do not get recreated when nothing changes in the nested rquirements files.
+    """
     # given
     tmpdir = tmpdir.strpath
     path = lambda *args: os.path.join(tmpdir, *args)
@@ -209,3 +215,8 @@ def update_file(fpath, content):
         os.makedirs(fdir)
     with open(fpath, 'w') as fd:
         fd.write(content)
+
+
+def read_text_file(fpath):
+    with open(fpath, 'r') as fd:
+        return fd.read()

toxbat/requirements.py

@@ -20,6 +20,7 @@
 
 # std
 import filecmp
+import hashlib
 import os
 import shutil
 
@@ -98,21 +99,20 @@ def is_changed(fpath, prev_version_fpath):
     new_requirements = parse_pip_requirements(fpath)
 
     # Hash them.
-    new_requirements_hash = hash(str(new_requirements))
+    new_requirements_hash = hashlib.sha1(str(new_requirements).encode('utf-8')).hexdigest()
 
     # Read the hash of the previous requirements if any.
     previous_requirements_hash = 0
     if os.path.exists(prev_version_fpath):
         with open(prev_version_fpath) as fd:
-            content = fd.read()
-            previous_requirements_hash = int(content)
+            previous_requirements_hash = fd.read()
 
     # Create/Update the file with the hash of the new requirements.
     dirname = os.path.dirname(prev_version_fpath)
     if not os.path.isdir(dirname):
         os.makedirs(dirname)
     with open(prev_version_fpath, 'w+') as fd:
-        fd.write(str(new_requirements_hash))
+        fd.write(new_requirements_hash)
 
     # Compare the hash of the new requirements with the hash of the previous requirements.
     return previous_requirements_hash != new_requirements_hash