fix more tests that fail if pandoc not installed

IPython/nbconvert/exporters/tests/test_slides.py

@@ -16,6 +16,7 b' Module with tests for slides.py'
 
 from .base import ExportersTestsBase
 from ..slides import SlidesExporter
+from IPython.testing.decorators import onlyif_cmds_exist
 
 #-----------------------------------------------------------------------------
 # Class
@@ -31,6 +32,7 b' class TestSlidesExporter(ExportersTestsBase):'
         SlidesExporter()
 
 
+    @onlyif_cmds_exist('pandoc')
     def test_export(self):
         """
         Can a SlidesExporter export something?
@@ -39,6 +41,7 b' class TestSlidesExporter(ExportersTestsBase):'
         assert len(output) > 0
 
 
+    @onlyif_cmds_exist('pandoc')
     def test_export_reveal(self):
         """
         Can a SlidesExporter export using the 'reveal' template?