add unittest for jpg, only activated if PIL/Pillow is installed

IPython/core/tests/test_pylabtools.py

@@ -53,6 +53,19 b' def test_figure_to_svg():'
     svg = pt.print_figure(fig, 'svg')[:100].lower()
     nt.assert_in(b'doctype svg', svg)
 
+try:
+    from PIL import Image
+    def test_figure_to_jpg():
+        # simple check for at least svg-looking output
+        fig = plt.figure()
+        ax = fig.add_subplot(1,1,1)
+        ax.plot([1,2,3])
+        plt.draw()
+        jpg = pt.print_figure(fig, 'jpg')[:100].lower()
+        assert jpg.startswith(b'\xff\xd8')
+except ImportError:
+    pass
+
 
 def test_import_pylab():
     ip = get_ipython()