Fix logic for longest_substring when only one input.

Tests added.

IPython/utils/tests/test_text.py

@@ -140,6 +140,16 b' def test_dollar_formatter():'
     nt.assert_equals(s, "$HOME")
 
 
+def test_long_substr():
+    data = ['hi']
+    nt.assert_equals(text.long_substr(data), 'hi')
+
+
+def test_long_substr2():
+    data = ['abc', 'abd', 'abf', 'ab']
+    nt.assert_equals(text.long_substr(data), 'ab')
+
+
 def test_strip_email():
     src = """\
         >> >>> def f(x):
@@ -152,3 +162,9 b' def test_strip_email():'
 ... 
 >>> zz = f(2.5)"""
     nt.assert_equals(text.strip_email_quotes(src), cln)
+
+
+def test_strip_email2():
+    src = '> > > list()'
+    cln = 'list()'
+    nt.assert_equals(text.strip_email_quotes(src), cln)

IPython/utils/text.py

@@ -553,6 +553,8 b' def long_substr(data):'
             for j in range(len(data[0])-i+1):
                 if j > len(substr) and all(data[0][i:i+j] in x for x in data):
                     substr = data[0][i:i+j]
+    else:
+        substr = data[0]
     return substr