in python, but need to change the default to Hz again for clean code and intuition

python/tests/test_freq.py

@@ -0,0 +1,14 @@
+from slsdet import Hz
+'''
+def test_Hz():
+    f = Hz(1)
+    assert f.value() == 1e6
+    f = Hz('1MHz')
+    assert f.value() == 1e6
+    f = Hz('5000kHz')
+    assert f.value() == 5e6
+    assert Hz(1) == 1
+    assert Hz(1e6) == 1e6
+    assert Hz(1, 'MHz') == 1e6
+    assert Hz(0.5, 'GHz') == 0.5e9
+'''