Index: tests/conftest.py
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
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+++ b/tests/conftest.py
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+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+import json
+
+import pytest
+
+from buildtools import packager
+
+MESSAGES_EN_US = json.dumps({
+    'name': {'message': 'Adblock Plus'},
+    'name_devbuild': {'message': 'devbuild-marker'},
+    'description': {
+        'message': 'Adblock Plus is the most popular ad blocker ever, '
+                   'and also supports websites by not blocking '
+                   'unobstrusive ads by default (configurable).'
+    },
+})
+
+
+@pytest.fixture(scope='module')
+def str500chars():
+    """Generates a String of 500 chars to simulate data"""
+    return b''.join(chr(i % 200 + 30) for i in range(500))
+
+
+@pytest.fixture
+def files(tmpdir, str500chars):
+    """Minimal Files() for testing all packagers."""
+    files = packager.Files(['lib'], set())
+    for size in ['44', '50', '150']:
+        files['Assets/logo_{}.png'.format(size)] = str500chars
+    files['Extension/_locales/en_US/messages.json'] = MESSAGES_EN_US
+    files['_locales/en_US/messages.json'] = MESSAGES_EN_US
+    files['Extension/foo.xml'] = str500chars
+    files['Extension/bar.png'] = str500chars * 200
+    files['lib/a.js'] = 'var bar;'
+    files['lib/b.js'] = 'var foo;'
+
+    lib_dir = tmpdir.mkdir('lib')
+
+    lib_dir.join('a.js').write(files['lib/a.js'])
+    lib_dir.join('b.js').write(files['lib/b.js'])
+    return files
+
+
+@pytest.fixture
+def srcdir(tmpdir):
+    """Source directory for building the package."""
+    for size in ['44', '50', '150']:
+        path = tmpdir.join('chrome', 'icons', 'abp-{}.png'.format(size))
+        path.write(size, ensure=True)
+
+    localedir = tmpdir.mkdir('_locales')
+    en_us_dir = localedir.mkdir('en_US')
+    trans_dir = localedir.mkdir('en-US')
+    en_us_dir.join('messages.json').write(MESSAGES_EN_US)
+
+    trans_dir.join('test.properties').write(''.join((
+        'name=Adblock Plus\n',
+        'name_devbuild=devbuild-marker\n',
+    )))
+    return tmpdir