1 new changeset in pytest:
http://bitbucket.org/hpk42/pytest/changeset/8c0df2a3ee3a/
changeset: 8c0df2a3ee3a
user: flub
date: 2011-06-20 14:18:12
summary: Add pytest_assertrepr_compare() docs
affected #: 1 file (3.9 KB)
--- a/doc/assert.txt Sat Jun 18 22:30:46 2011 +0200
+++ b/doc/assert.txt Mon Jun 20 14:18:12 2011 +0200
@@ -197,8 +197,112 @@
Introduce the ``--assertmode`` option. Deprecate ``--no-assert`` and
``--nomagic``.
-..
- Defining your own comparison
- ----------------------------------------------
+Defining your own comparison
+----------------------------------------------
+
+As already shown in examples py.test is able to provide detailed
+explanations when an assertial fails. E.g. when comparing a
+dictionary it will show you which elements differ::
+
+ $ py.test example.py
+ ============================= test session starts ==========================
+ platform linux2 -- Python 2.7.1 -- pytest-2.0.3
+ collected 1 items
+
+ example.py F
+
+ =================================== FAILURES ===============================
+ __________________________________ test_text _______________________________
+
+ def test_text():
+ > assert {'foo': 0, 'bar': 1} == {'foo': 0, 'bar': 0}
+ E assert {'bar': 1, 'foo': 0} == {'bar': 0, 'foo': 0}
+ E - {'bar': 1, 'foo': 0}
+ E ? ^
+ E + {'bar': 0, 'foo': 0}
+ E ? ^
+
+ example.py:2: AssertionError
+ =========================== 1 failed in 0.03 seconds =======================
+
+
+py.test has builtin knowledge about displaying detailed information
+for a number of types. If the objects compared do not match those it
+will fall back to a less detailed genric comparison, e.g.::
+
+ $ py.test example2.py
+ ============================= test session starts ==========================
+ platform linux2 -- Python 2.7.1 -- pytest-2.0.3
+ collected 1 items
+
+ example2.py F
+
+ =================================== FAILURES ===============================
+ ________________________________ test_foo __________________________________
+
+ def test_foo():
+ f = Foo(1)
+ g = Foo(2)
+ > assert f == g
+ E assert <example2.Foo object at 0x190de90> == <example2.Foo object
at 0x190df10>
+
+ example2.py:24: AssertionError
+ =========================== 1 failed in 0.03 seconds =======================
+
+
+The detailed builtin comparisons are currently only present for
+strings, sequences, sets and dictionaries which are compared for
+equality (``==``) and for strings with a ``not in`` comparison.
+However it is possible to add your own detailed explanations using the
+``pytest_assertrepr_compare`` hook.
+
+.. py:function:: pytest_assertrepr_compare(config, op, left, right)
+
+ The *config* argument is a ``_pytest.config.Config``
+ instance. *op* will be the comparison operator: ``==``, ``<``,
+ ``in``, etc. While *left* and *right* will contain the objects
+ which are being compared.
+
+ The return value must be either *None* in case this hook does not
+ provide an explanation for the arguments passed in, or a list of
+ strings. Each string in the list will be regarded as a line and
+ displayed on a line by itself. The first line is slightly special
+ and is meant to be a summary with the detailed explanation
+ following on the other lines.
+
+
+As an example consider adding following hook in a conftest.py which
+provides an alternative explanation for the ``Foo`` type used above::
+
+ def pytest_assertrepr_compare(op, left, right):
+ if (not isinstance(left, example2.Foo) or
+ not isinstance(right, example2.Foo) or
+ op != '=='):
+ return None
+ return ['Comparing Foo instances:',
+ ' vals: %s != %s' % (left.val, right.val)]
+
+When re-running the above example after adding this in the conftest.py
+file the output now contains a more detailed description::
+
+ $ python pytest.py example2.py
+ ============================= test session starts ==========================
+ platform linux2 -- Python 2.7.1 -- pytest-2.1.0.dev4
+ collected 1 items
+
+ example2.py F
+
+ =================================== FAILURES ===============================
+ ___________________________________ test_foo _______________________________
+
+ def test_foo():
+ f = Foo(1)
+ g = Foo(2)
+ > assert f == g
+ E assert Comparing Foo instances:
+ E vals: 1 != 2
+
+ example2.py:24: AssertionError
+ =========================== 1 failed in 0.03 seconds =======================
Repository URL: https://bitbucket.org/hpk42/pytest/
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