From afe9fd5ffd4486121d16ff2a434807822bc4b06c Mon Sep 17 00:00:00 2001
From: Arel Cordero <acordero@gmail.com>
Date: Thu, 24 Jan 2019 21:53:14 +0000
Subject: [PATCH] Adds `does_not_raise` context manager

Addressing issues #4324 and #1830
---
 AUTHORS                   |  1 +
 src/_pytest/python_api.py | 30 +++++++++++++++++++++++++++++
 src/pytest.py             |  2 ++
 testing/python/raises.py  | 40 +++++++++++++++++++++++++++++++++++++++
 4 files changed, 73 insertions(+)

diff --git a/AUTHORS b/AUTHORS
index 5c8cd9c9e..a4a41c942 100644
--- a/AUTHORS
+++ b/AUTHORS
@@ -27,6 +27,7 @@ Anthony Shaw
 Anthony Sottile
 Anton Lodder
 Antony Lee
+Arel Cordero
 Armin Rigo
 Aron Coyle
 Aron Curzon
diff --git a/src/_pytest/python_api.py b/src/_pytest/python_api.py
index 9b31d4e68..8babe13bf 100644
--- a/src/_pytest/python_api.py
+++ b/src/_pytest/python_api.py
@@ -4,6 +4,7 @@ import math
 import pprint
 import sys
 import warnings
+from contextlib import contextmanager
 from decimal import Decimal
 from numbers import Number
 
@@ -726,3 +727,32 @@ class RaisesContext(object):
         if self.match_expr is not None and suppress_exception:
             self.excinfo.match(self.match_expr)
         return suppress_exception
+
+
+# builtin pytest.does_not_raise helper
+
+
+@contextmanager
+def does_not_raise():
+    r"""
+    This context manager is a complement to ``pytest.raises()`` that does
+    *not* catch any exceptions raised by the code block.
+
+
+    This is essentially a no-op but is useful when
+    conditionally parameterizing tests that may or may not
+    raise an error. For example::
+
+        @pytest.mark.parametrize('example_input,expectation', [
+            (3, does_not_raise()),
+            (2, does_not_raise()),
+            (1, does_not_raise()),
+            (0, raises(ZeroDivisionError)),
+        ])
+        def test_division(example_input, expectation):
+            '''Test how much I know division.'''
+            with expectation:
+                assert (6 / example_input) is not None
+    """
+
+    yield
diff --git a/src/pytest.py b/src/pytest.py
index c0010f166..16ce2ad70 100644
--- a/src/pytest.py
+++ b/src/pytest.py
@@ -32,6 +32,7 @@ from _pytest.python import Instance
 from _pytest.python import Module
 from _pytest.python import Package
 from _pytest.python_api import approx
+from _pytest.python_api import does_not_raise
 from _pytest.python_api import raises
 from _pytest.recwarn import deprecated_call
 from _pytest.recwarn import warns
@@ -50,6 +51,7 @@ __all__ = [
     "cmdline",
     "Collector",
     "deprecated_call",
+    "does_not_raise",
     "exit",
     "fail",
     "File",
diff --git a/testing/python/raises.py b/testing/python/raises.py
index 4ff0b51bc..4ba9c1ccb 100644
--- a/testing/python/raises.py
+++ b/testing/python/raises.py
@@ -94,6 +94,46 @@ class TestRaises(object):
         result = testdir.runpytest()
         result.stdout.fnmatch_lines(["*3 passed*"])
 
+    def test_does_not_raise(self, testdir):
+        testdir.makepyfile(
+            """
+            import pytest
+            import _pytest._code
+
+            @pytest.mark.parametrize('example_input,expectation', [
+                (3, pytest.does_not_raise()),
+                (2, pytest.does_not_raise()),
+                (1, pytest.does_not_raise()),
+                (0, pytest.raises(ZeroDivisionError)),
+            ])
+            def test_division(example_input, expectation):
+                '''Test how much I know division.'''
+                with expectation:
+                    assert (6 / example_input) is not None
+        """
+        )
+        result = testdir.runpytest()
+        result.stdout.fnmatch_lines(["*4 passed*"])
+
+    def test_does_not_raise_does_raise(self, testdir):
+        testdir.makepyfile(
+            """
+            import pytest
+            import _pytest._code
+
+            @pytest.mark.parametrize('example_input,expectation', [
+                (0, pytest.does_not_raise()),
+                (1, pytest.raises(ZeroDivisionError)),
+            ])
+            def test_division(example_input, expectation):
+                '''Test how much I know division.'''
+                with expectation:
+                    assert (6 / example_input) is not None
+        """
+        )
+        result = testdir.runpytest()
+        result.stdout.fnmatch_lines(["*2 failed*"])
+
     def test_noclass(self):
         with pytest.raises(TypeError):
             pytest.raises("wrong", lambda: None)