Fix state leakage and speedup in test-suite

This is mostly visible when running the test via pytest that
collect-then-run vs nose that runs as it collects.

While I was at it I've improved some tests to be faster by changing the
maximum recursion limit.

IPython/core/tests/test_run.py

@@ -35,7 +35,6 b' from IPython.utils.io import capture_output'
 from IPython.utils.tempdir import TemporaryDirectory
 from IPython.core import debugger
 
-
 def doctest_refbug():
     """Very nasty problem with references held by multiple runs of a script.
     See: https://github.com/ipython/ipython/issues/141
@@ -537,6 +536,8 b' def test_run_tb():'
         nt.assert_not_in("execfile", out)
         nt.assert_in("RuntimeError", out)
         nt.assert_equal(out.count("---->"), 3)
+        del ip.user_ns['bar']
+        del ip.user_ns['foo']
 
 @dec.knownfailureif(sys.platform == 'win32', "writes to io.stdout aren't captured on Windows")
 def test_script_tb():

IPython/core/tests/test_ultratb.py

@@ -10,7 +10,8 b' import traceback'
 import unittest
 from unittest import mock
 
-from ..ultratb import ColorTB, VerboseTB, find_recursion
+import IPython.core.ultratb as ultratb
+from IPython.core.ultratb import ColorTB, VerboseTB, find_recursion
 
 
 from IPython.testing import tools as tt
@@ -18,8 +19,6 b' from IPython.testing.decorators import onlyif_unicode_paths'
 from IPython.utils.syspathcontext import prepended_to_syspath
 from IPython.utils.tempdir import TemporaryDirectory
 
-ip = get_ipython()
-
 file_1 = """1
 2
 3
@@ -31,6 +30,30 b' file_2 = """def f():'
   1/0
 """
 
+
+def recursionlimit(frames):
+    """
+    decorator to set the recursion limit temporarily
+    """
+
+    def inner(test_function):
+        def wrapper(*args, **kwargs):
+            _orig_rec_limit = ultratb._FRAME_RECURSION_LIMIT
+            ultratb._FRAME_RECURSION_LIMIT = frames - 50
+
+            rl = sys.getrecursionlimit()
+            sys.setrecursionlimit(frames)
+            try:
+                return test_function(*args, **kwargs)
+            finally:
+                sys.setrecursionlimit(rl)
+                ultratb._FRAME_RECURSION_LIMIT = _orig_rec_limit
+
+        return wrapper
+
+    return inner
+
+
 class ChangedPyFileTest(unittest.TestCase):
     def test_changing_py_file(self):
         """Traceback produced if the line where the error occurred is missing?
@@ -200,6 +223,8 b' bar()'
         # Assert syntax error during runtime generate stacktrace
         with tt.AssertPrints(["foo()", "bar()"]):
             ip.run_cell(syntax_error_at_runtime)
+        del ip.user_ns['bar']
+        del ip.user_ns['foo']
 
     def test_changing_py_file(self):
         with TemporaryDirectory() as td:
@@ -302,14 +327,17 b' def r3o2():'
         with tt.AssertNotPrints("frames repeated"):
             ip.run_cell("non_recurs()")
 
+    @recursionlimit(65)
     def test_recursion_one_frame(self):
         with tt.AssertPrints("1 frames repeated"):
             ip.run_cell("r1()")
 
+    @recursionlimit(65)
     def test_recursion_three_frames(self):
         with tt.AssertPrints("3 frames repeated"):
             ip.run_cell("r3o2()")
 
+    @recursionlimit(65)
     def test_find_recursion(self):
         captured = []
         def capture_exc(*args, **kwargs):

IPython/core/ultratb.py

@@ -137,6 +137,12 b' INDENT_SIZE = 8'
 # to users of ultratb who are NOT running inside ipython.
 DEFAULT_SCHEME = 'NoColor'
 
+
+# Number of frame above which we are likely to have a recursion and will
+# **attempt** to detect it.  Made modifiable mostly to speedup test suite
+# as detecting recursion is one of our slowest test
+_FRAME_RECURSION_LIMIT = 500
+
 # ---------------------------------------------------------------------------
 # Code begins
 
@@ -431,7 +437,7 b' def is_recursion_error(etype, value, records):'
     # a recursion error.
     return (etype is recursion_error_type) \
            and "recursion" in str(value).lower() \
-           and len(records) > 500
+           and len(records) > _FRAME_RECURSION_LIMIT
 
 def find_recursion(etype, value, records):
     """Identify the repeating stack frames from a RecursionError traceback

IPython/extensions/tests/test_storemagic.py

@@ -3,10 +3,13 b' import tempfile, os'
 from traitlets.config.loader import Config
 import nose.tools as nt
 
-ip = get_ipython()
+
+def setup_module():
 ip.magic('load_ext storemagic')
 
 def test_store_restore():
+    assert 'bar' not in ip.user_ns, "Error: some other test leaked `bar` in user_ns"
+    assert 'foo' not in ip.user_ns, "Error: some other test leaked `foo` in user_ns"
     ip.user_ns['foo'] = 78
     ip.magic('alias bar echo "hello"')
     tmpd = tempfile.mkdtemp()