Managing pytest’s output

Modifying Python traceback printing

Examples for modifying traceback printing:

pytest --showlocals # show local variables in tracebacks
pytest -l           # show local variables (shortcut)

pytest --tb=auto    # (default) 'long' tracebacks for the first and last
                     # entry, but 'short' style for the other entries
pytest --tb=long    # exhaustive, informative traceback formatting
pytest --tb=short   # shorter traceback format
pytest --tb=line    # only one line per failure
pytest --tb=native  # Python standard library formatting
pytest --tb=no      # no traceback at all

The --full-trace causes very long traces to be printed on error (longer than --tb=long). It also ensures that a stack trace is printed on KeyboardInterrupt (Ctrl+C). This is very useful if the tests are taking too long and you interrupt them with Ctrl+C to find out where the tests are hanging. By default no output will be shown (because KeyboardInterrupt is caught by pytest). By using this option you make sure a trace is shown.

Verbosity

The -v flag controls the verbosity of pytest output in various aspects: test session progress, assertion details when tests fail, fixtures details with --fixtures, etc.

Consider this simple file:

# content of test_verbosity_example.py
def test_ok():
    pass


def test_words_fail():
    fruits1 = ["banana", "apple", "grapes", "melon", "kiwi"]
    fruits2 = ["banana", "apple", "orange", "melon", "kiwi"]
    assert fruits1 == fruits2


def test_numbers_fail():
    number_to_text1 = {str(x): x for x in range(5)}
    number_to_text2 = {str(x * 10): x * 10 for x in range(5)}
    assert number_to_text1 == number_to_text2


def test_long_text_fail():
    long_text = "Lorem ipsum dolor sit amet " * 10
    assert "hello world" in long_text

Executing pytest normally gives us this output (we are skipping the header to focus on the rest):

$ pytest --no-header
=========================== test session starts ===========================
collected 4 items

test_verbosity_example.py .FFF                                       [100%]

================================ FAILURES =================================
_____________________________ test_words_fail _____________________________

    def test_words_fail():
        fruits1 = ["banana", "apple", "grapes", "melon", "kiwi"]
        fruits2 = ["banana", "apple", "orange", "melon", "kiwi"]
>       assert fruits1 == fruits2
E       AssertionError: assert ['banana', 'a...elon', 'kiwi'] == ['banana', 'a...elon', 'kiwi']
E         At index 2 diff: 'grapes' != 'orange'
E         Use -v to get the full diff

test_verbosity_example.py:8: AssertionError
____________________________ test_numbers_fail ____________________________

    def test_numbers_fail():
        number_to_text1 = {str(x): x for x in range(5)}
        number_to_text2 = {str(x * 10): x * 10 for x in range(5)}
>       assert number_to_text1 == number_to_text2
E       AssertionError: assert {'0': 0, '1':..., '3': 3, ...} == {'0': 0, '10'...'30': 30, ...}
E         Omitting 1 identical items, use -vv to show
E         Left contains 4 more items:
E         {'1': 1, '2': 2, '3': 3, '4': 4}
E         Right contains 4 more items:
E         {'10': 10, '20': 20, '30': 30, '40': 40}
E         Use -v to get the full diff

test_verbosity_example.py:14: AssertionError
___________________________ test_long_text_fail ___________________________

    def test_long_text_fail():
        long_text = "Lorem ipsum dolor sit amet " * 10
>       assert "hello world" in long_text
E       AssertionError: assert 'hello world' in 'Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ips... sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet '

test_verbosity_example.py:19: AssertionError
========================= short test summary info =========================
FAILED test_verbosity_example.py::test_words_fail - AssertionError: asser...
FAILED test_verbosity_example.py::test_numbers_fail - AssertionError: ass...
FAILED test_verbosity_example.py::test_long_text_fail - AssertionError: a...
======================= 3 failed, 1 passed in 0.08s =======================

Notice that:

  • Each test inside the file is shown by a single character in the output: . for passing, F for failure.

  • test_words_fail failed, and we are shown a short summary indicating the index 2 of the two lists differ.

  • test_numbers_fail failed, and we are shown a summary of left/right differences on dictionary items. Identical items are omitted.

  • test_long_text_fail failed, and the right hand side of the in statement is truncated using ...` because it is longer than an internal threshold (240 characters currently).

Now we can increase pytest’s verbosity:

$ pytest --no-header -v
=========================== test session starts ===========================
collecting ... collected 4 items

test_verbosity_example.py::test_ok PASSED                            [ 25%]
test_verbosity_example.py::test_words_fail FAILED                    [ 50%]
test_verbosity_example.py::test_numbers_fail FAILED                  [ 75%]
test_verbosity_example.py::test_long_text_fail FAILED                [100%]

================================ FAILURES =================================
_____________________________ test_words_fail _____________________________

    def test_words_fail():
        fruits1 = ["banana", "apple", "grapes", "melon", "kiwi"]
        fruits2 = ["banana", "apple", "orange", "melon", "kiwi"]
>       assert fruits1 == fruits2
E       AssertionError: assert ['banana', 'a...elon', 'kiwi'] == ['banana', 'a...elon', 'kiwi']
E         At index 2 diff: 'grapes' != 'orange'
E         Full diff:
E         - ['banana', 'apple', 'orange', 'melon', 'kiwi']
E         ?                      ^  ^^
E         + ['banana', 'apple', 'grapes', 'melon', 'kiwi']
E         ?                      ^  ^ +

test_verbosity_example.py:8: AssertionError
____________________________ test_numbers_fail ____________________________

    def test_numbers_fail():
        number_to_text1 = {str(x): x for x in range(5)}
        number_to_text2 = {str(x * 10): x * 10 for x in range(5)}
>       assert number_to_text1 == number_to_text2
E       AssertionError: assert {'0': 0, '1':..., '3': 3, ...} == {'0': 0, '10'...'30': 30, ...}
E         Omitting 1 identical items, use -vv to show
E         Left contains 4 more items:
E         {'1': 1, '2': 2, '3': 3, '4': 4}
E         Right contains 4 more items:
E         {'10': 10, '20': 20, '30': 30, '40': 40}
E         Full diff:
E         - {'0': 0, '10': 10, '20': 20, '30': 30, '40': 40}...
E
E         ...Full output truncated (3 lines hidden), use '-vv' to show

test_verbosity_example.py:14: AssertionError
___________________________ test_long_text_fail ___________________________

    def test_long_text_fail():
        long_text = "Lorem ipsum dolor sit amet " * 10
>       assert "hello world" in long_text
E       AssertionError: assert 'hello world' in 'Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet '

test_verbosity_example.py:19: AssertionError
========================= short test summary info =========================
FAILED test_verbosity_example.py::test_words_fail - AssertionError: asser...
FAILED test_verbosity_example.py::test_numbers_fail - AssertionError: ass...
FAILED test_verbosity_example.py::test_long_text_fail - AssertionError: a...
======================= 3 failed, 1 passed in 0.07s =======================

Notice now that:

  • Each test inside the file gets its own line in the output.

  • test_words_fail now shows the two failing lists in full, in addition to which index differs.

  • test_numbers_fail now shows a text diff of the two dictionaries, truncated.

  • test_long_text_fail no longer truncates the right hand side of the in statement, because the internal threshold for truncation is larger now (2400 characters currently).

Now if we increase verbosity even more:

$ pytest --no-header -vv
=========================== test session starts ===========================
collecting ... collected 4 items

test_verbosity_example.py::test_ok PASSED                            [ 25%]
test_verbosity_example.py::test_words_fail FAILED                    [ 50%]
test_verbosity_example.py::test_numbers_fail FAILED                  [ 75%]
test_verbosity_example.py::test_long_text_fail FAILED                [100%]

================================ FAILURES =================================
_____________________________ test_words_fail _____________________________

    def test_words_fail():
        fruits1 = ["banana", "apple", "grapes", "melon", "kiwi"]
        fruits2 = ["banana", "apple", "orange", "melon", "kiwi"]
>       assert fruits1 == fruits2
E       AssertionError: assert ['banana', 'apple', 'grapes', 'melon', 'kiwi'] == ['banana', 'apple', 'orange', 'melon', 'kiwi']
E         At index 2 diff: 'grapes' != 'orange'
E         Full diff:
E         - ['banana', 'apple', 'orange', 'melon', 'kiwi']
E         ?                      ^  ^^
E         + ['banana', 'apple', 'grapes', 'melon', 'kiwi']
E         ?                      ^  ^ +

test_verbosity_example.py:8: AssertionError
____________________________ test_numbers_fail ____________________________

    def test_numbers_fail():
        number_to_text1 = {str(x): x for x in range(5)}
        number_to_text2 = {str(x * 10): x * 10 for x in range(5)}
>       assert number_to_text1 == number_to_text2
E       AssertionError: assert {'0': 0, '1': 1, '2': 2, '3': 3, '4': 4} == {'0': 0, '10': 10, '20': 20, '30': 30, '40': 40}
E         Common items:
E         {'0': 0}
E         Left contains 4 more items:
E         {'1': 1, '2': 2, '3': 3, '4': 4}
E         Right contains 4 more items:
E         {'10': 10, '20': 20, '30': 30, '40': 40}
E         Full diff:
E         - {'0': 0, '10': 10, '20': 20, '30': 30, '40': 40}
E         ?            -    -    -    -    -    -    -    -
E         + {'0': 0, '1': 1, '2': 2, '3': 3, '4': 4}

test_verbosity_example.py:14: AssertionError
___________________________ test_long_text_fail ___________________________

    def test_long_text_fail():
        long_text = "Lorem ipsum dolor sit amet " * 10
>       assert "hello world" in long_text
E       AssertionError: assert 'hello world' in 'Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet Lorem ipsum dolor sit amet '

test_verbosity_example.py:19: AssertionError
========================= short test summary info =========================
FAILED test_verbosity_example.py::test_words_fail - AssertionError: asser...
FAILED test_verbosity_example.py::test_numbers_fail - AssertionError: ass...
FAILED test_verbosity_example.py::test_long_text_fail - AssertionError: a...
======================= 3 failed, 1 passed in 0.07s =======================

Notice now that:

  • Each test inside the file gets its own line in the output.

  • test_words_fail gives the same output as before in this case.

  • test_numbers_fail now shows a full text diff of the two dictionaries.

  • test_long_text_fail also doesn’t truncate on the right hand side as before, but now pytest won’t truncate any text at all, regardless of its size.

Those were examples of how verbosity affects normal test session output, but verbosity also is used in other situations, for example you are shown even fixtures that start with _ if you use pytest --fixtures -v.

Using higher verbosity levels (-vvv, -vvvv, …) is supported, but has no effect in pytest itself at the moment, however some plugins might make use of higher verbosity.

Producing a detailed summary report

The -r flag can be used to display a “short test summary info” at the end of the test session, making it easy in large test suites to get a clear picture of all failures, skips, xfails, etc.

It defaults to fE to list failures and errors.

Example:

# content of test_example.py
import pytest


@pytest.fixture
def error_fixture():
    assert 0


def test_ok():
    print("ok")


def test_fail():
    assert 0


def test_error(error_fixture):
    pass


def test_skip():
    pytest.skip("skipping this test")


def test_xfail():
    pytest.xfail("xfailing this test")


@pytest.mark.xfail(reason="always xfail")
def test_xpass():
    pass
$ pytest -ra
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-6.x.y, py-1.x.y, pluggy-1.x.y
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collected 6 items

test_example.py .FEsxX                                               [100%]

================================== ERRORS ==================================
_______________________ ERROR at setup of test_error _______________________

    @pytest.fixture
    def error_fixture():
>       assert 0
E       assert 0

test_example.py:6: AssertionError
================================= FAILURES =================================
________________________________ test_fail _________________________________

    def test_fail():
>       assert 0
E       assert 0

test_example.py:14: AssertionError
========================= short test summary info ==========================
SKIPPED [1] test_example.py:22: skipping this test
XFAIL test_example.py::test_xfail
  reason: xfailing this test
XPASS test_example.py::test_xpass always xfail
ERROR test_example.py::test_error - assert 0
FAILED test_example.py::test_fail - assert 0
== 1 failed, 1 passed, 1 skipped, 1 xfailed, 1 xpassed, 1 error in 0.12s ===

The -r options accepts a number of characters after it, with a used above meaning “all except passes”.

Here is the full list of available characters that can be used:

  • f - failed

  • E - error

  • s - skipped

  • x - xfailed

  • X - xpassed

  • p - passed

  • P - passed with output

Special characters for (de)selection of groups:

  • a - all except pP

  • A - all

  • N - none, this can be used to display nothing (since fE is the default)

More than one character can be used, so for example to only see failed and skipped tests, you can execute:

$ pytest -rfs
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-6.x.y, py-1.x.y, pluggy-1.x.y
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collected 6 items

test_example.py .FEsxX                                               [100%]

================================== ERRORS ==================================
_______________________ ERROR at setup of test_error _______________________

    @pytest.fixture
    def error_fixture():
>       assert 0
E       assert 0

test_example.py:6: AssertionError
================================= FAILURES =================================
________________________________ test_fail _________________________________

    def test_fail():
>       assert 0
E       assert 0

test_example.py:14: AssertionError
========================= short test summary info ==========================
FAILED test_example.py::test_fail - assert 0
SKIPPED [1] test_example.py:22: skipping this test
== 1 failed, 1 passed, 1 skipped, 1 xfailed, 1 xpassed, 1 error in 0.12s ===

Using p lists the passing tests, whilst P adds an extra section “PASSES” with those tests that passed but had captured output:

$ pytest -rpP
=========================== test session starts ============================
platform linux -- Python 3.x.y, pytest-6.x.y, py-1.x.y, pluggy-1.x.y
cachedir: $PYTHON_PREFIX/.pytest_cache
rootdir: $REGENDOC_TMPDIR
collected 6 items

test_example.py .FEsxX                                               [100%]

================================== ERRORS ==================================
_______________________ ERROR at setup of test_error _______________________

    @pytest.fixture
    def error_fixture():
>       assert 0
E       assert 0

test_example.py:6: AssertionError
================================= FAILURES =================================
________________________________ test_fail _________________________________

    def test_fail():
>       assert 0
E       assert 0

test_example.py:14: AssertionError
================================== PASSES ==================================
_________________________________ test_ok __________________________________
--------------------------- Captured stdout call ---------------------------
ok
========================= short test summary info ==========================
PASSED test_example.py::test_ok
== 1 failed, 1 passed, 1 skipped, 1 xfailed, 1 xpassed, 1 error in 0.12s ===

Creating resultlog format files

To create plain-text machine-readable result files you can issue:

pytest --resultlog=path

and look at the content at the path location. Such files are used e.g. by the PyPy-test web page to show test results over several revisions.

Warning

This option is rarely used and is scheduled for removal in pytest 6.0.

If you use this option, consider using the new pytest-reportlog plugin instead.

See the deprecation docs for more information.

Creating JUnitXML format files

To create result files which can be read by Jenkins or other Continuous integration servers, use this invocation:

pytest --junitxml=path

to create an XML file at path.

To set the name of the root test suite xml item, you can configure the junit_suite_name option in your config file:

[pytest]
junit_suite_name = my_suite

New in version 4.0.

JUnit XML specification seems to indicate that "time" attribute should report total test execution times, including setup and teardown (1, 2). It is the default pytest behavior. To report just call durations instead, configure the junit_duration_report option like this:

[pytest]
junit_duration_report = call

record_property

If you want to log additional information for a test, you can use the record_property fixture:

def test_function(record_property):
    record_property("example_key", 1)
    assert True

This will add an extra property example_key="1" to the generated testcase tag:

<testcase classname="test_function" file="test_function.py" line="0" name="test_function" time="0.0009">
  <properties>
    <property name="example_key" value="1" />
  </properties>
</testcase>

Alternatively, you can integrate this functionality with custom markers:

# content of conftest.py


def pytest_collection_modifyitems(session, config, items):
    for item in items:
        for marker in item.iter_markers(name="test_id"):
            test_id = marker.args[0]
            item.user_properties.append(("test_id", test_id))

And in your tests:

# content of test_function.py
import pytest


@pytest.mark.test_id(1501)
def test_function():
    assert True

Will result in:

<testcase classname="test_function" file="test_function.py" line="0" name="test_function" time="0.0009">
  <properties>
    <property name="test_id" value="1501" />
  </properties>
</testcase>

Warning

Please note that using this feature will break schema verifications for the latest JUnitXML schema. This might be a problem when used with some CI servers.

record_xml_attribute

To add an additional xml attribute to a testcase element, you can use record_xml_attribute fixture. This can also be used to override existing values:

def test_function(record_xml_attribute):
    record_xml_attribute("assertions", "REQ-1234")
    record_xml_attribute("classname", "custom_classname")
    print("hello world")
    assert True

Unlike record_property, this will not add a new child element. Instead, this will add an attribute assertions="REQ-1234" inside the generated testcase tag and override the default classname with "classname=custom_classname":

<testcase classname="custom_classname" file="test_function.py" line="0" name="test_function" time="0.003" assertions="REQ-1234">
    <system-out>
        hello world
    </system-out>
</testcase>

Warning

record_xml_attribute is an experimental feature, and its interface might be replaced by something more powerful and general in future versions. The functionality per-se will be kept, however.

Using this over record_xml_property can help when using ci tools to parse the xml report. However, some parsers are quite strict about the elements and attributes that are allowed. Many tools use an xsd schema (like the example below) to validate incoming xml. Make sure you are using attribute names that are allowed by your parser.

Below is the Scheme used by Jenkins to validate the XML report:

<xs:element name="testcase">
    <xs:complexType>
        <xs:sequence>
            <xs:element ref="skipped" minOccurs="0" maxOccurs="1"/>
            <xs:element ref="error" minOccurs="0" maxOccurs="unbounded"/>
            <xs:element ref="failure" minOccurs="0" maxOccurs="unbounded"/>
            <xs:element ref="system-out" minOccurs="0" maxOccurs="unbounded"/>
            <xs:element ref="system-err" minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="name" type="xs:string" use="required"/>
        <xs:attribute name="assertions" type="xs:string" use="optional"/>
        <xs:attribute name="time" type="xs:string" use="optional"/>
        <xs:attribute name="classname" type="xs:string" use="optional"/>
        <xs:attribute name="status" type="xs:string" use="optional"/>
    </xs:complexType>
</xs:element>

Warning

Please note that using this feature will break schema verifications for the latest JUnitXML schema. This might be a problem when used with some CI servers.

record_testsuite_property

New in version 4.5.

If you want to add a properties node at the test-suite level, which may contains properties that are relevant to all tests, you can use the record_testsuite_property session-scoped fixture:

The record_testsuite_property session-scoped fixture can be used to add properties relevant to all tests.

import pytest


@pytest.fixture(scope="session", autouse=True)
def log_global_env_facts(record_testsuite_property):
    record_testsuite_property("ARCH", "PPC")
    record_testsuite_property("STORAGE_TYPE", "CEPH")


class TestMe:
    def test_foo(self):
        assert True

The fixture is a callable which receives name and value of a <property> tag added at the test-suite level of the generated xml:

<testsuite errors="0" failures="0" name="pytest" skipped="0" tests="1" time="0.006">
  <properties>
    <property name="ARCH" value="PPC"/>
    <property name="STORAGE_TYPE" value="CEPH"/>
  </properties>
  <testcase classname="test_me.TestMe" file="test_me.py" line="16" name="test_foo" time="0.000243663787842"/>
</testsuite>

name must be a string, value will be converted to a string and properly xml-escaped.

The generated XML is compatible with the latest xunit standard, contrary to record_property and record_xml_attribute.

Sending test report to an online pastebin service

Creating a URL for each test failure:

pytest --pastebin=failed

This will submit test run information to a remote Paste service and provide a URL for each failure. You may select tests as usual or add for example -x if you only want to send one particular failure.

Creating a URL for a whole test session log:

pytest --pastebin=all

Currently only pasting to the https://bpaste.net/ service is implemented.

Changed in version 5.2.

If creating the URL fails for any reason, a warning is generated instead of failing the entire test suite.