[baseline] Easy String Baseline¶
This tool streamlines creation and maintenance of tests which compare string output against a baseline. It offers a mechanism to compare a string against a baselined copy and update the baselined copy to match the new value when a mismatch occurs. The update process includes a manual step to facilitate a review of the change before acceptance. The tool uses multi-line string format for string baselines to improve readability for human review.
Quick Start¶
Create an empty baseline with a triple quoted multi-line string. Place
the ending triple quote on a separate line and indent it to the level
you wish the string baseline update to be indented to. Add a compare of
the string being tested to the baseline string. Then save the file as
fox.py
:
from baseline import Baseline
expected = Baseline("""
""")
test_string = """THE QUICK BROWN FOX
JUMPS
OVER THE LAZY DOG."""
assert test_string == expected
Run fox.py
and observe that the assert
raises an exception since
the strings are not equal. Because the comparison failed, the tool located
the triple quoted baseline string in the source file and updated it with the
mis-compared value. When the interpreter exited, the tool saved the updated
source file but changed the file name to fox.py.update
:
from baseline import Baseline
expected = Baseline("""
THE QUICK BROWN FOX
JUMPS
OVER THE LAZY DOG.
""")
test_string = """THE QUICK BROWN FOX
JUMPS
OVER THE LAZY DOG."""
assert test_string == expected
After reviewing the change with your favorite file differencing tool,
accept the change by either manually overwriting the original file or use
the baseline
command line tool to scan the directory for updated
scripts:
$ python -m baseline *
Found baseline updates for:
fox.py
Hit [ENTER] to accept, [Ctrl-C] to cancel
Pressing Enter
causes the tool to overwrite the scripts with
the new baseline updates and remove the temporary .py.update
files.
Run fox.py
again and observe the assert
does not raise an exception
nor is a copy of the source file update generated. If in the future the test
value changes, the assert
raises an exception and causes a new source file
update to be generated. Simply repeat the review and acceptance step and you
are back in business!
[baseline] About¶
Contributors¶
- Dan Gass (dan.gass at gmail dot com)
- Primary author
- Adam Karpierz (akarpierz at gmail dot com)
- Python 3 support
- Packaging
- Peter Gessler (gessler.pd at gmail dot com)
- Travis C/I Setup
Development¶
Repository: | https://github.com/dmgass/baseline |
---|
License¶
MIT License
Copyright (c) 2018 Daniel Mark Gass (dan.gass@gmail.com)
Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.
[baseline] API Reference¶
Classes¶
-
class
baseline.
Baseline
¶ Baseline string.
Support comparison of a string against this baseline. When the comparison results in a mismatch, make a copy of the Python script containing the baseline and modify the baseline to match the new value.
Command Line¶
$ python -m baseline --help
usage: baseline [-h] [-w] [path [path ...]]
Locate scripts with baseline updates within the paths specified and modify the
scripts with the updates found. (The scripts to be modified will be summarized
and you will be offered a chance to cancel before files are changed.)
positional arguments:
path module or directory path
optional arguments:
-h, --help show this help message and exit
-w, --walk recursively walk directories
[baseline] Installation¶
Prerequisites¶
-
- version 2.7
- version 3.4 or higher
Requirements for Installing Packages (located in the Installing Packages tutorial within the Python Packaging User Guide).
[baseline] Release Notes¶
Versions increment per semver.
Note
Changes to experimental features only result in a bump of the subminor (patch) version, including those introducing backwards incompatibility.
1.2.1 2020-DEC-26¶
- Fix
baseline
command line interface support for specifying directories to search. Previously, baseline inadvertently raised an exception if a directory other than the default ('.'
) was specified.
1.2.0 2020-DEC-22¶
- Add
--force
command line option to suppress acknowledgement prompt. - Add Python 3.9 support advertisement. (Regression testing added to release process.)
- Remove Python 3.4 and 3.5 support advertisement. (Regression testing removed from release process.) Nothing blocks installation, but no promise exists that the package works with those interpreter versions.
1.1.2 2020-MAY-02¶
- Maintain file permissions and owner (both when generating update file and when applying update file to original script). Previously, file owner and permissions were set based on permission levels of execution context which caused issues when executing under elevated permission levels (e.g. sudo).
1.1.1 2020-MAY-02¶
- Improve experimental feature to support specifying an alternative
location. Add
BASELINE_MOVE_UPDATES
environment variable that when set toYES
, enables specifying an alternative location to write update files. This master switch facilitates allowing CI/CD systems to enable the feature while leaving the feature off in local development while still using CI/CD resources (e.g. tox).
1.1.0 2020-MAY-01¶
- Add
--clean
(-c) option to baseline command line tool to remove update files. - Add
--diff
(-d) option to baseline command line tool that shows difference and queries for overwrite permission for each updated file. - Change update file extension to
.py.update
so that testing frameworks such asunittest
orpytest
ignore them. - Add experimental feature to support specifying an alternative
location to write update files with the
BASELINE_UPDATES_PATH
environment variable. (Note,BASELINE_RELPATH_BASE
must be set when using this feature.) - Add experimental feature to print contextual differences whenever
a baseline mis-compare occurs. The feature may be turned on by
setting the environment variable (
BASELINE_PRINT_DIFFS="YES"
) or overriding the class attribute (Baseline.PRINT_DIFFS = True
).
1.0.0 2020-MAR-19¶
- Improve baseline update when multiple values compared against the same baseline. Generate a single multi-line baseline with headers between the various alternative values. This facilitates updating the baseline again.
- Support Python 3.8. Previously, when run using 3.8, the baseline update tool misplaced baseline updates in the first triple quoted string found above the baseline. (Python 3.8 stack frames now report the line number of the first line in a statement rather than the last.)
- Change behavior of
Baseline
to use raw strings when updating baselines when possible and improves readability. - Deprecate
RawBaseline
sinceBaseline
now incorporates its behavior.
Beta Releases¶
- 0.2.1 (2018-05-19)
- Fix command line tool to not raise UnboundedLocalError exception. Previously when tool was invoked with a wild card that yielded no baseline updates to move, an exception was unexpectedly raised.
- 0.2.0 (2018-05-18)
- Add
--movepath
command line option to move updated scripts to a new location instead of overwriting the original script (for use in continuous integration systems performing regression tests).
- Add
- 0.1.3 (2018-03-29)
- Show command line help dump in API reference documentation.
- Fix development status classifier in setup configuration (to make PyPi listing accurate).
- 0.1.2 (2018-03-27)
- Add Travis C/I support.
- Change author name to commonly used form.
- Use Python 3.5 in tox for basic tasks.
- Remove “beta” label.
- 0.1.1 (2018-03-25)
- Change author to match PyPi user name.
- 0.1.0 (2018-03-25)
- Initial “beta” release.
[baseline] Usage¶
One line Strings¶
To create a baseline string that contains a special update mechanism,
use triple quotes around the string and instantiate Baseline
with it. The resulting Python string object supports natural equality
comparisons:
from baseline import Baseline
expected = Baseline("""Hello""")
test_string = "Hello World!"
assert test_string == expected
Run the script and observe that the assert
raises an exception since
the strings are not equal. Because the comparison failed, the tool located
the triple quoted baseline string in the source file and updated it with the
miscompared value. When the interpretter exited, the tool saved the updated
source file using the file extension .py.update
):
expected = Baseline("""Hello World!""")
test_string = "Hello World!"
assert test_string == expected
After reviewing the change with your favorite file differencing tool,
accept the change by either manually overwriting the original file or use
the baseline
command line interface to scan the directory for baseline
update files:
$ python -m baseline *
Found baseline updates for:
hello.py
Hit [ENTER] to update, [Ctrl-C] to cancel
Pressing Enter causes the tool to overwrite the scripts with the new baseline updates and remove the temporary .py.update files.
Multi-Line Strings¶
The triple quote usage in the Baseline
instantiation provides a
consistent search and replace mechanism that supports embedding quotation
marks and newlines within a baselined string. Embedding newlines improves
the strings human readability which makes reviewing updates easier.
For multiline baselined string format, start the string on the line following the opening triple quote delimiter. Insert a line after the baselined string content to hold the closing triple quote delimiter. Indent the closing triple quote delimiter to the indentation level of the baselined string:
from baseline import Baseline
expected = Baseline("""
THE QUICK BROWN FOX
JUMPS
OVER THE LAZY DOG.
""")
test_string = "THE QUICK BROWN FOX\n JUMPS\nOVER THE LAZY DOG."
assert test_string == expected
The example above executes without an assertion because the tool strips the leading indentation of every line in the baselined string based on the indentation of the closing triple quote.
Transforms¶
Often strings to test against a baseline contain substrings that may vary from one execution to the next. Before the comparison, normalize the string by substituting a representative constant value. For example, use a regular expression to transform a variable time into a constant value:
import re
import time
from baseline import Baseline
expected = Baseline("""The time is HH:MM:SS.""")
test_string = "The time is {}.".format(time.strftime("%H:%M:%S"))
assert re.sub(r'\d\d:\d\d:\d\d', 'HH:MM:SS', test_string) == expected
If this is a common operation or there are multiple transformations needed,
override the TRANSFORMS
class attribute and list the operations to
be performed. The tool performs each of the operations on the test string
before every comparison.
import re
import time
from baseline import Baseline
def normalize_time(s):
return re.sub(r'\d\d:\d\d:\d\d', 'HH:MM:SS', s)
class NormalizedBaseline(Baseline):
"""Normalized string baseline."""
TRANSFORMS = [normalize_time]
expected = NormalizedBaseline("""The time is HH:MM:SS.""")
test_string = "The time is {}.".format(time.strftime("%H:%M:%S"))
assert test_string == expected
Tips and Tricks¶
Quick Tips¶
- Take your time and be diligent in your review of baseline updates. Similar to Python itself, this tool provides a lot of rope, don’t hang yourself.
- Put comments above the baseline to provide information to a future maintainer of the important aspects of the baseline that are the focus of the test.
- Feel free to baseline strings with any style triple quotes embedded. The tool adjusts and uses the alternative style. If the test string contains both styles, transform one style into something else before comparison.
- To archive resulting test script updates from a regression test run
within a continuous integration system, use the
--movepath
command line option to move updated scripts to a new location instead of overwriting the original script. T
Initial Baseline Value¶
To avoid the work of anticipating the exact content of the string baseline, specify an empty baseline in multi-line format and set the indentation level with the closing triple quote:
from baseline import Baseline
expected = Baseline("""
""")
test_string = "THE QUICK BROWN FOX\n JUMPS\nOVER THE LAZY DOG."
assert test_string == expected
Run the script and let the tool fill in the string baseline. Then carefully review the baseline update and accept.