Add test for deprecated decorator

Author: tpoliaw

tests/unit_tests/utils/test_deprecated.py

@@ -0,0 +1,19 @@
+import warnings
+
+import pytest
+
+from blueapi.utils import deprecated
+
+
+def test_deprecated_annotation():
+    @deprecated("bar")
+    def foo():
+        return 1
+
+    with pytest.warns(DeprecationWarning, match="Function foo is deprecated - use bar"):
+        assert foo() == 1
+
+    # The second time a function is called, the warning should not be raised
+    with warnings.catch_warnings():
+        warnings.simplefilter("error")
+        assert foo() == 1