diff --git a/tests/test_elm_package.py b/tests/test_elm_package.py
new file mode 100644
index 0000000..46a5138
--- /dev/null
+++ b/tests/test_elm_package.py
@@ -0,0 +1,10 @@
+import elm_package
+
+
+def test_sync_deps_messages_when_version_is_changed():
+    from_deps = {'core': '1.0.0'}
+    to_deps = {'core': '0.1.0'}
+
+    messages, new_deps = elm_package.sync_deps(from_deps, to_deps)
+    assert len(messages) == 1
+    assert '0.1.0 to 1.0.0' in messages[0]