Fixed various issues with test imports (#3995)

holoviews/tests/core/testdatasetproperty.py

@@ -12,7 +12,11 @@
 from holoviews.core import Apply, Redim
 from holoviews.element.comparison import ComparisonTestCase
 from holoviews.operation import histogram
-from holoviews.operation.datashader import dynspread, datashade, rasterize
+
+try:
+    from holoviews.operation.datashader import dynspread, datashade, rasterize
+except:
+    dynspread = datashade = rasterize = None
 
 
 
@@ -715,6 +719,11 @@ def test_distribution_dataset(self):
 
 class DatashaderTestCase(DatasetPropertyTestCase):
 
+    def setUp(self):
+        if None in (rasterize, datashade, dynspread):
+            raise SkipTest('Datashader could not be imported and cannot be tested.')
+        super(DatashaderTestCase, self).setUp()
+
     def test_rasterize_curve(self):
         img = rasterize(
             self.ds.to(Curve, 'a', 'b', groupby=[]), dynamic=False

holoviews/tests/plotting/plotly/testcallbacks.py

@@ -12,11 +12,14 @@
 except:
     go = None
 
-from holoviews.plotting.plotly.callbacks import (
-    RangeXYCallback, RangeXCallback, RangeYCallback,
-    BoundsXYCallback, BoundsXCallback, BoundsYCallback,
-    Selection1DCallback
-)
+try:
+    from holoviews.plotting.plotly.callbacks import (
+        RangeXYCallback, RangeXCallback, RangeYCallback,
+        BoundsXYCallback, BoundsXCallback, BoundsYCallback,
+        Selection1DCallback
+    )
+except:
+    pass
 
 
 def mock_plot(trace_uid=None):

holoviews/tests/plotting/plotly/testrenderer.py

@@ -27,7 +27,7 @@
 class PlotlyRendererTest(ComparisonTestCase):
 
     def setUp(self):
-        if 'plotly' not in Store.renderers and None not in (pn, PlotlyRenderer):
+        if 'plotly' not in Store.renderers or None in (pn, PlotlyRenderer):
             raise SkipTest("Plotly and Panel required to test rendering.")
 
         self.previous_backend = Store.current_backend