Add failing test for suppressing exception chaining

IPython/core/tests/test_ultratb.py

@@ -1,184 +1,197 b''
 # encoding: utf-8
 """Tests for IPython.core.ultratb
 """
 import io
 import os.path
 import unittest
 
 from IPython.testing import tools as tt
 from IPython.testing.decorators import onlyif_unicode_paths
 from IPython.utils.syspathcontext import prepended_to_syspath
 from IPython.utils.tempdir import TemporaryDirectory
 from IPython.utils.py3compat import PY3
 
 ip = get_ipython()
 
 file_1 = """1
 2
 3
 def f():
   1/0
 """
 
 file_2 = """def f():
   1/0
 """
 
 class ChangedPyFileTest(unittest.TestCase):
     def test_changing_py_file(self):
         """Traceback produced if the line where the error occurred is missing?
         
         https://github.com/ipython/ipython/issues/1456
         """
         with TemporaryDirectory() as td:
             fname = os.path.join(td, "foo.py")
             with open(fname, "w") as f:
                 f.write(file_1)
             
             with prepended_to_syspath(td):
                 ip.run_cell("import foo")
             
             with tt.AssertPrints("ZeroDivisionError"):
                 ip.run_cell("foo.f()")
             
             # Make the file shorter, so the line of the error is missing.
             with open(fname, "w") as f:
                 f.write(file_2)
             
             # For some reason, this was failing on the *second* call after
             # changing the file, so we call f() twice.
             with tt.AssertNotPrints("Internal Python error", channel='stderr'):
                 with tt.AssertPrints("ZeroDivisionError"):
                     ip.run_cell("foo.f()")
                 with tt.AssertPrints("ZeroDivisionError"):
                     ip.run_cell("foo.f()")
 
 iso_8859_5_file = u'''# coding: iso-8859-5
 
 def fail():
     """дбИЖ"""
     1/0     # дбИЖ
 '''
 
 class NonAsciiTest(unittest.TestCase):
     @onlyif_unicode_paths
     def test_nonascii_path(self):
         # Non-ascii directory name as well.
         with TemporaryDirectory(suffix=u'é') as td:
             fname = os.path.join(td, u"fooé.py")
             with open(fname, "w") as f:
                 f.write(file_1)
             
             with prepended_to_syspath(td):
                 ip.run_cell("import foo")
             
             with tt.AssertPrints("ZeroDivisionError"):
                 ip.run_cell("foo.f()")
     
     def test_iso8859_5(self):
         with TemporaryDirectory() as td:
             fname = os.path.join(td, 'dfghjkl.py')
 
             with io.open(fname, 'w', encoding='iso-8859-5') as f:
                 f.write(iso_8859_5_file)
             
             with prepended_to_syspath(td):
                 ip.run_cell("from dfghjkl import fail")
             
             with tt.AssertPrints("ZeroDivisionError"):
                 with tt.AssertPrints(u'дбИЖ', suppress=False):
                     ip.run_cell('fail()')
 
 indentationerror_file = """if True:
 zoon()
 """
 
 class IndentationErrorTest(unittest.TestCase):
     def test_indentationerror_shows_line(self):
         # See issue gh-2398
         with tt.AssertPrints("IndentationError"):
             with tt.AssertPrints("zoon()", suppress=False):
                 ip.run_cell(indentationerror_file)
         
         with TemporaryDirectory() as td:
             fname = os.path.join(td, "foo.py")
             with open(fname, "w") as f:
                 f.write(indentationerror_file)
             
             with tt.AssertPrints("IndentationError"):
                 with tt.AssertPrints("zoon()", suppress=False):
                     ip.magic('run %s' % fname)
 
 se_file_1 = """1
 2
 7/
 """
 
 se_file_2 = """7/
 """
 
 class SyntaxErrorTest(unittest.TestCase):
     def test_syntaxerror_without_lineno(self):
         with tt.AssertNotPrints("TypeError"):
             with tt.AssertPrints("line unknown"):
                 ip.run_cell("raise SyntaxError()")
 
     def test_changing_py_file(self):
         with TemporaryDirectory() as td:
             fname = os.path.join(td, "foo.py")
             with open(fname, 'w') as f:
                 f.write(se_file_1)
 
             with tt.AssertPrints(["7/", "SyntaxError"]):
                 ip.magic("run " + fname)
 
             # Modify the file
             with open(fname, 'w') as f:
                 f.write(se_file_2)
 
             # The SyntaxError should point to the correct line
             with tt.AssertPrints(["7/", "SyntaxError"]):
                 ip.magic("run " + fname)
 
     def test_non_syntaxerror(self):
         # SyntaxTB may be called with an error other than a SyntaxError
         # See e.g. gh-4361
         try:
             raise ValueError('QWERTY')
         except ValueError:
             with tt.AssertPrints('QWERTY'):
                 ip.showsyntaxerror()
 
 
 class Python3ChainedExceptionsTest(unittest.TestCase):
     DIRECT_CAUSE_ERROR_CODE = """
 try:
     x = 1 + 2
     print(not_defined_here)
 except Exception as e:
     x += 55
     x - 1
     y = {}
     raise KeyError('uh') from e
     """
 
     EXCEPTION_DURING_HANDLING_CODE = """
 try:
     x = 1 + 2
     print(not_defined_here)
 except Exception as e:
     x += 55
     x - 1
     y = {}
     raise KeyError('uh')
     """
 
+    SUPPRESS_CHAINING_CODE = """
+try:
+    1/0
+except Exception:
+    raise ValueError("Yikes") from None
+    """
+
     def test_direct_cause_error(self):
         if PY3:
             with tt.AssertPrints(["KeyError", "NameError", "direct cause"]):
                 ip.run_cell(self.DIRECT_CAUSE_ERROR_CODE)
 
     def test_exception_during_handling_error(self):
         if PY3:
             with tt.AssertPrints(["KeyError", "NameError", "During handling"]):
                 ip.run_cell(self.EXCEPTION_DURING_HANDLING_CODE)
+
+    def test_suppress_exception_chaining(self):
+        if PY3:
+            with tt.AssertNotPrints("ZeroDivisionError"), \
+                    tt.AssertPrints("ValueError", suppress=False):
+                ip.run_cell(self.SUPPRESS_CHAINING_CODE)