fix test

IPython/core/magics/basic.py

@@ -601,6 +601,8 b' Defaulting color scheme to \'NoColor\'"""'
         if args.export:
             cells = []
             hist = list(self.shell.history_manager.get_range())
+            if(len(hist)<=1):
+                raise ValueError('History is empty, cannot export')
             for session, execution_count, input in hist[:-1]:
                 cells.append(v4.new_code_cell(
                     execution_count=execution_count,

IPython/core/tests/test_magic.py

@@ -623,9 +623,13 b' def test_extension():'
 @skipIf(dec.module_not_available('IPython.nbformat'), 'nbformat not importable')
 class NotebookExportMagicTests(TestCase):
     def test_notebook_export_json(self):
+        _ip = get_ipython()
+        _ip.history_manager.reset()   # Clear any existing history.
+        cmds = [u"a=1", u"def b():\n  return a**2", u"print(a, b())"]
+        for i, cmd in enumerate(cmds, start=1):
+            _ip.history_manager.store_inputs(i, cmd)
         with TemporaryDirectory() as td:
             outfile = os.path.join(td, "nb.ipynb")
-            _ip.ex(py3compat.u_format(u"u = {u}'héllo'"))
             _ip.magic("notebook -e %s" % outfile)