add deprecator test

Author: cadenmyers13

tests/test_deprecator.py

@@ -0,0 +1,37 @@
+import pytest
+
+from diffpy.utils._deprecator import deprecated, deprecation_message
+
+old_base = "diffpy.utils"
+old_name = "oldFunction"
+new_name = "new_function"
+removal_version = "4.0.0"
+
+dep_msg = deprecation_message(old_base, old_name, new_name, removal_version)
+
+
+@deprecated(dep_msg)
+def oldFunction(print_msg):
+    """This function is deprecated and will be removed in version 4.0.0.
+
+    Please use newFunction instead
+    """
+    return new_function(print_msg)
+
+
+def new_function(print_msg):
+    print(print_msg)
+    return
+
+
+def test_deprecated(capsys):
+    # Case: user deprecates a function with the deprecated decorator
+    # Expected: DeprecationWarning is raised when the function is called
+    #           and the function executes correctly
+    expected_print_msg = "Testing deprecated function"
+    with pytest.deprecated_call(match=dep_msg):
+        oldFunction(expected_print_msg)
+
+    captured = capsys.readouterr()
+    actual_print_msg = captured.out.strip()
+    assert actual_print_msg == expected_print_msg