add test for dt.timer

tests/test_dt.py

@@ -0,0 +1,23 @@
+import os
+from pydu.dt import timer
+
+
+class TestTimer(object):
+    def test_context_manager(self):
+        timeit = timer()
+
+        with timeit:
+            os.getcwd()
+
+        assert timeit.elapsed is not None
+
+    def test_decorator(self):
+        import sys
+        timeit = timer(print_func=print)
+
+        @timeit
+        def foo():
+            os.getcwd()
+
+        foo()
+        assert timeit.elapsed is not None