Large code refactoring

* Add tests
* Remove git dependency (only needed when a git identifier is specified)

tests/functional/test_multiple_calls.py

@@ -0,0 +1,23 @@
+import unittest
+
+from django_migration_linter import MigrationLinter
+from tests import fixtures
+
+class TestMultipleLinters(unittest.TestCase):
+    def test_multiple_linters(self):
+        l1 = MigrationLinter(fixtures.ADD_NOT_NULL_COLUMN_PROJECT)
+        l2 = MigrationLinter(fixtures.RENAME_COLUMN_PROJECT)
+        l3 = MigrationLinter(fixtures.CORRECT_PROJECT)
+
+        l1.lint_migration('test_app', '0002')
+        l2.lint_migration('test_app', '0002')
+        l3.lint_migration('test_app1', '0001')
+        l3.lint_migration('test_app1', '0002')
+
+        self.assertTrue(l1.has_errors)
+        self.assertTrue(l2.has_errors)
+        self.assertFalse(l3.has_errors)
+
+        self.assertEqual(l1.nb_total, 1)
+        self.assertEqual(l2.nb_total, 1)
+        self.assertEqual(l3.nb_total, 2)