minor changes doc and comments

mth5/timeseries/spectre/spectrogram.py

@@ -19,16 +19,19 @@ class Spectrogram(object):
 
     """
 
-    def __init__(self, dataset=None):
+    def __init__(
+        self,
+        dataset: Optional[xr.Dataset] = None
+    ):
         """Constructor"""
         self._dataset = dataset
         self._frequency_increment = None
 
-    def _lowest_frequency(self):
+    def _lowest_frequency(self):  # -> float:
         pass  # return self.dataset.frequency.min
 
-    def _highest_frequency(self):
-        pass
+    def _highest_frequency(self):  # -> float:
+        pass  # return self.dataset.frequency.max
 
     def __str__(self) -> str:
         """Returns a Description of frequency coverage"""

tests/version_1/test_fcs.py

@@ -383,8 +383,9 @@ def test_from_xarray_dtypes(self):
 
     def test_multi_station_spectrogram(self):
         """
-        TODO: This could be moved to fc_tools.
-        It is here because there was a handy dataset already available here.
+        TODO: This should have its own test in tests/spectre/test_multiple_station.py
+         It can be moved once there is a fixture available for the dataset in the test_fcs.py module.
+         See Issue #227.
 
         """
         fc_run_chunks = []
@@ -400,7 +401,6 @@ def test_multi_station_spectrogram(self):
             )
             fc_run_chunks.append(fcrc)
 
-        # TODO: These tests should go in their own module, but need test dataset (issue #227)
         xrds = make_multistation_spectrogram(self.m, fc_run_chunks, rtype="xrds")