Add a test for preinstalled data directory checking

.travis.yml

@@ -13,7 +13,8 @@ install:
   - python -m pip install -U pip wheel setuptools
   - python -m pip install -U isort flake8
   - python -m pip install -r requirements.txt
-  - python -m pip install -e .
+  - python -Wd setup.py sdist
+  - python -Wd -m pip install dist/py3-validate-email-*.tar.gz
 
 # command to run tests
 script:

tests/test_install.py

@@ -0,0 +1,28 @@
+from pathlib import Path
+from subprocess import check_output
+from unittest.case import TestCase
+
+try:
+    # OSX Homebrew fix: https://stackoverflow.com/a/53190037/1067833
+    from sys import _base_executable as executable
+except ImportError:
+    from sys import executable
+
+
+class InstallTest(TestCase):
+    'Testing package installation.'
+
+    def test_datadir_is_in_place(self):
+        'Data directory should be in the virtualenv.'
+        output = check_output([
+            executable, '-c', (
+                'import sys;sys.path.remove("");import validate_email;'
+                'print(validate_email.updater.BLACKLIST_FILEPATH_INSTALLED);'
+                'print(validate_email.updater.ETAG_FILEPATH_INSTALLED, end="")'
+            )]).decode('ascii')
+        bl_path, etag_path = output.split('\n')
+        self.assertTrue(
+            expr=Path(bl_path).exists(), msg=f'{bl_path!r} doesn\'t exist.')
+        self.assertTrue(
+            expr=Path(etag_path).exists(),
+            msg=f'{etag_path!r} doesn\'t exist.')