Add tests for custom pdb class.

(and edit CHANGELOG)

CHANGELOG.rst

@@ -116,7 +116,8 @@
   Example '-o xfail_strict=True'. A complete ini-options can be viewed
   by py.test --help. Thanks `@blueyed`_ and `@fengxx`_ for the PR
 
-*
+* Allow passing a custom debugger class (e.g. ``IPython.core.debugger:Pdb``
+  via ``--pdbcls``).  Thanks to `@anntzer`_ for the PR.
 
 *
 
@@ -185,8 +186,7 @@
   Before, you only got exceptions later from ``argparse`` library,
   giving no clue about the actual reason for double-added options.
 
-* Allow passing a custom debugger class (e.g. ``IPython.core.debugger:Pdb``
+*
-  via ``--pdbcls``.
 
 *
 
@@ -266,6 +266,7 @@
 .. _@DRMacIver: https://github.com/DRMacIver
 .. _@RedBeardCode: https://github.com/RedBeardCode
 .. _@Vogtinator: https://github.com/Vogtinator
+.. _@anntzer: https://github.com/anntzer
 .. _@bagerard: https://github.com/bagerard
 .. _@blueyed: https://github.com/blueyed
 .. _@ceridwen: https://github.com/ceridwen

_pytest/debugging.py

@@ -13,7 +13,8 @@ def pytest_addoption(parser):
         help="start the interactive Python debugger on errors.")
     group._addoption(
         '--pdbcls', dest="usepdb_cls", metavar="modulename:classname",
-        help="start a custom interactive Python debugger on errors.")
+        help="start a custom interactive Python debugger on errors. "
+             "For example: --pdbcls=IPython.core.debugger:Pdb")
 
 def pytest_namespace():
     return {'set_trace': pytestPDB().set_trace}

testing/test_pdb.py

@@ -311,3 +311,28 @@ class TestPDB:
         child.sendeof()
         if child.isalive():
             child.wait()
+
+    def test_pdb_custom_cls(self, testdir):
+        called = []
+
+        # install dummy debugger class and track which methods were called on it
+        class _CustomPdb:
+            def __init__(self, *args, **kwargs):
+                called.append("init")
+
+            def reset(self):
+                called.append("reset")
+
+            def interaction(self, *args):
+                called.append("interaction")
+
+        _pytest._CustomPdb = _CustomPdb
+
+        p1 = testdir.makepyfile("""xxx """)
+        result = testdir.runpytest_inprocess(
+            "--pdbcls=_pytest:_CustomPdb", p1)
+        result.stdout.fnmatch_lines([
+            "*NameError*xxx*",
+            "*1 error*",
+        ])
+        assert called == ["init", "reset", "interaction"]