Fixed broken import in typecaster.h (#1181)

- Fixed the broken import _slsdet --> slsdet._slsdet caused by a previous upgrade
- Added tests that exercises the conversion from python to C++ and from C++ to python
- Python unit tests now run in CI (!)

python/tests/test_DurationWrapper.py

@@ -0,0 +1,58 @@
+import pytest
+
+from slsdet import DurationWrapper
+
+#import the compiled extension to use test functions for the automatic conversion
+from slsdet import _slsdet
+
+
+def test_default_construction_of_DurationWrapper():
+    """Test default construction of DurationWrapper"""
+    t = DurationWrapper()
+    assert t.count() == 0
+    assert t.total_seconds() == 0
+
+def test_construction_of_DurationWrapper():
+    """Test construction of DurationWrapper with total_seconds"""
+    t = DurationWrapper(5)
+    assert t.count() == 5e9
+    assert t.total_seconds() == 5
+
+def test_set_count_on_DurationWrapper():
+    """Test set_count on DurationWrapper"""
+    t = DurationWrapper()
+    t.set_count(10)
+    assert t.count() == 10
+    assert t.total_seconds() == 10e-9
+    t.set_count(0)
+    assert t.count() == 0
+    assert t.total_seconds() == 0
+
+
+def test_return_a_DurationWrapper_from_cpp():
+    """Test returning a DurationWrapper from C++"""
+    t = _slsdet.test_return_DurationWrapper()
+    assert t.count() == 1.3e9
+    assert t.total_seconds() == 1.3
+
+def test_call_a_cpp_function_with_a_duration_wrapper():
+    """C++ functions can accept a DurationWrapper"""
+    t = DurationWrapper(5)
+    assert _slsdet.test_duration_to_ns(t) == 5e9
+    
+def test_call_a_cpp_function_converting_number_to_DurationWrapper():
+    """int and float can be converted to std::chrono::nanoseconds"""
+    assert _slsdet.test_duration_to_ns(0) == 0
+    assert _slsdet.test_duration_to_ns(3) == 3e9
+    assert _slsdet.test_duration_to_ns(1.3) == 1.3e9
+    assert _slsdet.test_duration_to_ns(10e-9) == 10
+
+def test_call_a_cpp_function_with_datetime_timedelta():
+    """datetime.timedelta can be converted to std::chrono::nanoseconds"""
+    import datetime
+    t = datetime.timedelta(seconds=5)
+    assert _slsdet.test_duration_to_ns(t) == 5e9
+    t = datetime.timedelta(seconds=0)
+    assert _slsdet.test_duration_to_ns(t) == 0
+    t = datetime.timedelta(seconds=1.3)
+    assert _slsdet.test_duration_to_ns(t) == 1.3e9