move ipython command line logic to one place

it keeps getting repeated, more elegant to move it out into the call

IPython/nbconvert/tests/base.py

@@ -20,6 +20,13 b' import shutil'
 import IPython
 from IPython.utils.tempdir import TemporaryDirectory
 from IPython.utils.process import get_output_error_code
+from IPython.utils import py3compat
+
+# Define ipython command line name
+if py3compat.PY3:
+    ipy_cmd = 'ipython3 '
+else:
+    ipy_cmd = 'ipython '
 
 #-----------------------------------------------------------------------------
 # Classes and functions
@@ -165,7 +172,7 b' class TestsBase(object):'
 
 
     def call(self, parameters, raise_on_error=True):
-        stdout, stderr, retcode = get_output_error_code(parameters)
+        stdout, stderr, retcode = get_output_error_code(ipy_cmd + parameters)
         if retcode != 0 and raise_on_error:
             raise OSError(stderr)
         return stdout, stderr

IPython/nbconvert/tests/test_nbconvertapp.py

@@ -16,7 +16,6 b' Contains tests for the nbconvertapp'
 import os
 from .base import TestsBase
 
-from IPython.utils import py3compat
 from IPython.testing import decorators as dec
 
     
@@ -24,12 +23,6 b' from IPython.testing import decorators as dec'
 # Constants
 #-----------------------------------------------------------------------------
 
-# Define ipython commandline name
-if py3compat.PY3:
-    IPYTHON = 'ipython3'
-else:
-    IPYTHON = 'ipython'
-
 
 #-----------------------------------------------------------------------------
 # Classes and functions
@@ -44,7 +37,7 b' class TestNbConvertApp(TestsBase):'
         Will help show if no notebooks are specified?
         """
         with self.create_temp_cwd():
-            out, err = self.call(IPYTHON + ' nbconvert', raise_on_error=False)
+            out, err = self.call('nbconvert', raise_on_error=False)
             assert "see '--help-all'" in out
 
 
@@ -53,8 +46,7 b' class TestNbConvertApp(TestsBase):'
         Do search patterns work for notebook names?
         """
         with self.create_temp_cwd(['notebook*.ipynb']):
-            self.call(IPYTHON + ' nbconvert --to="python"'
-                       ' --notebooks=*.ipynb')
+            self.call('nbconvert --to="python" --notebooks=*.ipynb')
             assert os.path.isfile('notebook1.py')
             assert os.path.isfile('notebook2.py')
 
@@ -65,7 +57,7 b' class TestNbConvertApp(TestsBase):'
         """
         with self.create_temp_cwd():
             self.copy_files_to(['notebook*.ipynb'], 'subdir/')
-            self.call(IPYTHON + ' nbconvert --to="python"'
+            self.call('nbconvert --to="python"'
                       ' --notebooks=%s' % os.path.join('subdir', '*.ipynb'))
             assert os.path.isfile('notebook1.py')
             assert os.path.isfile('notebook2.py')
@@ -76,8 +68,7 b' class TestNbConvertApp(TestsBase):'
         Do explicit notebook names work?
         """
         with self.create_temp_cwd(['notebook*.ipynb']):
-            self.call(IPYTHON + ' nbconvert --to="python"'
-                      ' --notebooks=notebook2.ipynb')
+            self.call('nbconvert --to="python" --notebooks=notebook2.ipynb')
             assert not os.path.isfile('notebook1.py')
             assert os.path.isfile('notebook2.py')
 
@@ -89,8 +80,8 b' class TestNbConvertApp(TestsBase):'
         Do post processors work?
         """
         with self.create_temp_cwd(['notebook1.ipynb']):
-            self.call(IPYTHON + ' nbconvert --to="latex" notebook1'
-                       ' --post="PDF" --PDFPostProcessor.verbose=True')
+            self.call('nbconvert --to="latex" notebook1'
+                      ' --post="PDF" --PDFPostProcessor.verbose=True')
             assert os.path.isfile('notebook1.tex')
             print("\n\n\t" + "\n\t".join([f for f in os.listdir('.') if os.path.isfile(f)]) + "\n\n")
             assert os.path.isfile('notebook1.pdf')
@@ -102,9 +93,8 b' class TestNbConvertApp(TestsBase):'
         Do export templates work?
         """
         with self.create_temp_cwd(['notebook2.ipynb']):
-            self.call(IPYTHON + ' nbconvert --to=slides'
-                       ' --notebooks=notebook2.ipynb'
-                       ' --template=reveal')
+            self.call('nbconvert --to=slides --notebooks=notebook2.ipynb'
+                      ' --template=reveal')
             assert os.path.isfile('notebook2.slides.html')
             with open('notebook2.slides.html') as f:
                 assert '/reveal.css' in f.read()
@@ -115,7 +105,7 b' class TestNbConvertApp(TestsBase):'
         Can a search pattern be used along with matching explicit notebook names?
         """
         with self.create_temp_cwd(['notebook*.ipynb']):
-            self.call(IPYTHON + ' nbconvert --to="python" --notebooks='
+            self.call('nbconvert --to="python" --notebooks='
                       '*.ipynb,notebook1.ipynb,notebook2.ipynb')
             assert os.path.isfile('notebook1.py')
             assert os.path.isfile('notebook2.py')
@@ -126,7 +116,7 b' class TestNbConvertApp(TestsBase):'
         Can explicit notebook names be used and then a matching search pattern?
         """
         with self.create_temp_cwd(['notebook*.ipynb']):
-            self.call(IPYTHON + ' nbconvert --to="python" --notebooks='
+            self.call('nbconvert --to="python" --notebooks='
                       'notebook1.ipynb,notebook2.ipynb,*.ipynb')
             assert os.path.isfile('notebook1.py')
             assert os.path.isfile('notebook2.py')
@@ -137,7 +127,7 b' class TestNbConvertApp(TestsBase):'
         Does the default config work?
         """
         with self.create_temp_cwd(['notebook*.ipynb', 'ipython_nbconvert_config.py']):
-            self.call(IPYTHON + ' nbconvert')
+            self.call('nbconvert')
             assert os.path.isfile('notebook1.py')
             assert not os.path.isfile('notebook2.py')
 
@@ -149,6 +139,6 b' class TestNbConvertApp(TestsBase):'
         with self.create_temp_cwd(['notebook*.ipynb',
                                    'ipython_nbconvert_config.py',
                                    'override.py']):
-            self.call(IPYTHON + ' nbconvert --config="override.py"')
+            self.call('nbconvert --config="override.py"')
             assert not os.path.isfile('notebook1.py')
             assert os.path.isfile('notebook2.py')