fix for incorrect stats computation in diff exp t-test (#2318)

* 2211 fixes

* lint

* lint

* add missing test and bug found by test

* change terminology for count distribution

* update scanpy requirement

* update scanpy requirement

backend/server/data_common/data_adaptor.py

@@ -6,7 +6,7 @@ from scipy import sparse
 from server_timing import Timing as ServerTiming
 
 from backend.server.common.config.app_config import AppConfig
-from backend.common.constants import Axis
+from backend.common.constants import Axis, XApproxDistribution
 from backend.common.errors import FilterError, JSONEncodingValueError, ExceedsLimitError, UnsupportedSummaryMethod
 from backend.common.utils.utils import jsonify_numpy
 from backend.common.fbs.matrix import encode_matrix_fbs
@@ -72,6 +72,10 @@ class DataAdaptor(metaclass=ABCMeta):
         the return type is either ndarray or scipy.sparse.spmatrix."""
         pass
 
+    def get_X_approx_distribution(self) -> XApproxDistribution:
+        """return the approximate distribution of the X matrix."""
+        return XApproxDistribution.NORMAL
+
     @abstractmethod
     def get_shape(self):
         pass