Add unit test for version check

Author: bobleesj

tests/test_version.py

@@ -0,0 +1,10 @@
+"""Unit tests for __version__.py
+"""
+
+import diffpy.structure
+
+
+def test_package_version():
+    """Ensure the package version is defined and not set to the initial placeholder."""
+    assert hasattr(diffpy.structure, '__version__'), "The package version is not defined."
+    assert diffpy.structure.__version__ != "0.0.0"