Thanks to visit codestin.com
Credit goes to github.com

Skip to content

Commit e9e5dcd

Browse files
author
Skip Montanaro
committed
restructured a bit and added some more content...
1 parent 4d06923 commit e9e5dcd

1 file changed

Lines changed: 142 additions & 53 deletions

File tree

‎Lib/test/README‎

Lines changed: 142 additions & 53 deletions
Original file line numberDiff line numberDiff line change
@@ -1,40 +1,73 @@
1-
Writing Python Test Cases
2-
-------------------------
1+
Writing Python Regression Tests
2+
-------------------------------
33
Skip Montanaro
4+
([email protected])
5+
6+
7+
Introduction
48

59
If you add a new module to Python or modify the functionality of an existing
6-
module, it is your responsibility to write one or more test cases to test
7-
that new functionality. The mechanics of the test system are fairly
8-
straightforward. If you are writing test cases for module zyzzyx, you need
9-
to create a file in .../Lib/test named test_zyzzyx.py and an expected output
10-
file in .../Lib/test/output named test_zyzzyx ("..." represents the
11-
top-level directory in the Python source tree, the directory containing the
12-
configure script). Generate the initial version of the test output file by
13-
executing:
14-
15-
cd .../Lib/test
16-
python regrtest.py -g test_zyzzyx.py
17-
18-
Any time you modify test_zyzzyx.py you need to generate a new expected
10+
module, you should write one or more test cases to exercise that new
11+
functionality. The mechanics of how the test system operates are fairly
12+
straightforward. When a test case is run, the output is compared with the
13+
expected output that is stored in .../Lib/test/output. If the test runs to
14+
completion and the actual and expected outputs match, the test succeeds, if
15+
not, it fails. If an ImportError is raised, the test is not run.
16+
17+
You will be writing unit tests (isolated tests of functions and objects
18+
defined by the module) using white box techniques. Unlike black box
19+
testing, where you only have the external interfaces to guide your test case
20+
writing, in white box testing you can see the code being tested and tailor
21+
your test cases to exercise it more completely. In particular, you will be
22+
able to refer to the C and Python code in the CVS repository when writing
23+
your regression test cases.
24+
25+
26+
Executing Test Cases
27+
28+
If you are writing test cases for module spam, you need to create a file
29+
in .../Lib/test named test_spam.py and an expected output file in
30+
.../Lib/test/output named test_spam ("..." represents the top-level
31+
directory in the Python source tree, the directory containing the configure
32+
script). From the top-level directory, generate the initial version of the
33+
test output file by executing:
34+
35+
./python Lib/test/regrtest.py -g test_spam.py
36+
37+
Any time you modify test_spam.py you need to generate a new expected
1938
output file. Don't forget to desk check the generated output to make sure
2039
it's really what you expected to find! To run a single test after modifying
2140
a module, simply run regrtest.py without the -g flag:
2241

23-
cd .../Lib/test
24-
python regrtest.py test_zyzzyx.py
42+
./python Lib/test/regrtest.py test_spam.py
43+
44+
While debugging a regression test, you can of course execute it
45+
independently of the regression testing framework and see what it prints:
46+
47+
./python Lib/test/test_spam.py
2548

2649
To run the entire test suite, make the "test" target at the top level:
2750

28-
cd ...
2951
make test
3052

31-
Test cases generate output based upon computed values and branches taken in
32-
the code. When executed, regrtest.py compares the actual output generated
33-
by executing the test case with the expected output and reports success or
34-
failure. It stands to reason that if the actual and expected outputs are to
35-
match, they must not contain any machine dependencies. This means
36-
your test cases should not print out absolute machine addresses or floating
37-
point numbers with large numbers of significant digits.
53+
On non-Unix platforms where make may not be available, you can simply
54+
execute the two runs of regrtest (optimized and non-optimized) directly:
55+
56+
./python Lib/test/regrtest.py
57+
./python -O Lib/test/regrtest.py
58+
59+
60+
Test cases generate output based upon values computed by the test code.
61+
When executed, regrtest.py compares the actual output generated by executing
62+
the test case with the expected output and reports success or failure. It
63+
stands to reason that if the actual and expected outputs are to match, they
64+
must not contain any machine dependencies. This means your test cases
65+
should not print out absolute machine addresses (e.g. the return value of
66+
the id() builtin function) or floating point numbers with large numbers of
67+
significant digits (unless you understand what you are doing!).
68+
69+
70+
Test Case Writing Tips
3871

3972
Writing good test cases is a skilled task and is too complex to discuss in
4073
detail in this short document. Many books have been written on the subject.
@@ -46,32 +79,88 @@ object-oriented software revolution, so doesn't cover that subject at all.
4679
Unfortunately, it is very expensive (about $100 new). If you can borrow it
4780
or find it used (around $20), I strongly urge you to pick up a copy.
4881

49-
As an author of at least part of a module, you will be writing unit tests
50-
(isolated tests of functions and objects defined by the module) using white
51-
box techniques. (Unlike black box testing, where you only have the external
52-
interfaces to guide your test case writing, in white box testing you can see
53-
the code being tested and tailor your test cases to exercise it more
54-
completely).
55-
5682
The most important goal when writing test cases is to break things. A test
57-
case that doesn't uncover a bug is less valuable than one that does. In
58-
designing test cases you should pay attention to the following:
59-
60-
1. Your test cases should exercise all the functions and objects defined
61-
in the module, not just the ones meant to be called by users of your
62-
module. This may require you to write test code that uses the module
63-
in ways you don't expect (explicitly calling internal functions, for
64-
example - see test_atexit.py).
65-
66-
2. You should consider any boundary values that may tickle exceptional
67-
conditions (e.g. if you were testing a division module you might well
68-
want to generate tests with numerators and denominators at the limits
69-
of floating point and integer numbers on the machine performing the
70-
tests as well as a denominator of zero).
71-
72-
3. You should exercise as many paths through the code as possible. This
73-
may not always be possible, but is a goal to strive for. In
74-
particular, when considering if statements (or their equivalent), you
75-
want to create test cases that exercise both the true and false
76-
branches. For while and for statements, you should create test cases
77-
that exercise the loop zero, one and multiple times.
83+
case that doesn't uncover a bug is much less valuable than one that does.
84+
In designing test cases you should pay attention to the following:
85+
86+
* Your test cases should exercise all the functions and objects defined
87+
in the module, not just the ones meant to be called by users of your
88+
module. This may require you to write test code that uses the module
89+
in ways you don't expect (explicitly calling internal functions, for
90+
example - see test_atexit.py).
91+
92+
* You should consider any boundary values that may tickle exceptional
93+
conditions (e.g. if you were writing regression tests for division,
94+
you might well want to generate tests with numerators and denominators
95+
at the limits of floating point and integer numbers on the machine
96+
performing the tests as well as a denominator of zero).
97+
98+
* You should exercise as many paths through the code as possible. This
99+
may not always be possible, but is a goal to strive for. In
100+
particular, when considering if statements (or their equivalent), you
101+
want to create test cases that exercise both the true and false
102+
branches. For loops, you should create test cases that exercise the
103+
loop zero, one and multiple times.
104+
105+
* You should test with obviously invalid input. If you know that a
106+
function requires an integer input, try calling it with other types of
107+
objects to see how it responds.
108+
109+
* You should test with obviously out-of-range input. If the domain of a
110+
function is only defined for positive integers, try calling it with a
111+
negative integer.
112+
113+
* If you are going to fix a bug that wasn't uncovered by an existing
114+
test, try to write a test case that exposes the bug (preferably before
115+
fixing it).
116+
117+
118+
Regression Test Writing Rules
119+
120+
Each test case is different. There is no "standard" form for a Python
121+
regression test case, though there are some general rules:
122+
123+
* If your test case detects a failure, raise TestFailed (found in
124+
test_support).
125+
126+
* Import everything you'll need as early as possible.
127+
128+
* If you'll be importing objects from a module that is at least
129+
partially platform-dependent, only import those objects you need for
130+
the current test case to avoid spurious ImportError exceptions that
131+
prevent the test from running to completion.
132+
133+
* Print all your test case results using the print statement. For
134+
non-fatal errors, print an error message (or omit a successful
135+
completion print) to indicate the failure, but proceed instead of
136+
raising TestFailed.
137+
138+
139+
Miscellaneous
140+
141+
There is a test_support module you can import from your test case. It
142+
provides the following useful objects:
143+
144+
* TestFailed - raise this exception when your regression test detects a
145+
failure.
146+
147+
* findfile(file) - you can call this function to locate a file somewhere
148+
along sys.path or in the Lib/test tree - see test_linuxaudiodev.py for
149+
an example of its use.
150+
151+
* verbose - you can use this variable to control print output. Many
152+
modules use it. Search for "verbose" in the test_*.py files to see
153+
lots of examples.
154+
155+
* fcmp(x,y) - you can call this function to compare two floating point
156+
numbers when you expect them to only be approximately equal withing a
157+
fuzz factor (test_support.FUZZ, which defaults to 1e-6).
158+
159+
Python and C statement coverage results are currently available at
160+
161+
http://www.musi-cal.com/~skip/python/Python/dist/src/
162+
163+
As of this writing (July, 2000) these results are being generated nightly.
164+
You can refer to the summaries and the test coverage output files to see
165+
where coverage is adequate or lacking and write test cases to beef up the
166+
coverage.

0 commit comments

Comments
 (0)