graphpaper.py
(the module)
graphpaperunittest.py
To put the
graph paper
code into testable form,
I packaged it as the function
draw
in
line
7
of
graphpaper.py.
This function takes four
int
arguments and returns a
string
containing the graph paper.
Run
graphpaper.py
by itself to try out the function
by passing it arguments and printing its return value.
Class
TestGraphpaper
in
line
11
of
graphpaperunittest.py
is a
subclass
of class
unittest.TestCase.
That means that class
TestGraphpaper
has all the attributes and methods of class
unittest.TestCase,
plus more.
We say that class
TestGraphpaper
inherits
all the attributes and methods of its
superclass
unittest.TestCase.
Here are two examples.
It looks like class
TestGraphpaper
has only the three methods in lines
13,
24,
and
33.
But this class also has methods named
assertRaises
(lines
19
and
38)
and
assertEqual
(line
45),
which class
TestGraphpaper
inherits from class
unittest.TestCase.
The methods of class
TestGraphpaper
whose names begin with
test_
(lines
13,
24,
and
33)
are called automatically by the
unittest.main
function in
line
52.
The
test_
methods are executed in alphabetical order.
To get a different order,
we could have given them names like
test_001_return
test_002_type
test_003_range
The
list
comprehension
in
line
29
creates the
list
[1, 1, 1, 1].
The first time
line
30
is executed, it changes this list to
[0, 1, 1, 1].
These four ints are then passed to the
draw
function as four separate arguments using the asterisk we saw in
line
23
of
variablenumber.py
in
Variable
number.
The 0 is an illegal argument for
draw
and should make this function raise the
ValueError
exception.
The
with
in
line
28
makes the computer behave as if we had surrounded
lines
29–31
with
try
and
except.
In other words, the
with
will prevent any exception raised by
lines
29–31
from terminating the script.
On the other hand,
lines
29–31
(specifically,
line
31)
are supposed to raise a
ValueError
exception because of the bad argument 0.
If these lines do not raise the exception,
the
assertRaises
method in
line
28
will report an error in the final output of the script.
The lines under the
with
(lines
29–31)
must not contain any lines after the line that raises the exception
(line
31).
Any line after the line that raises the exception would never be executed.
I wanted to include
True
and
False
in the
tuple
of arguments of illegal (i.e., non-integer) data types in
line
16.
But it turned out that
True
and
False
were actually integers in disguise, so they were legal.
Save
graphpaper.py
and
graphpaperunittest.py
in the directory that holds all your other Python scripts.
Open
graphpaperunittest.py
in an IDLE window
(by pulling down File → Open…)
and run it
(by pulling down Run → Run Module).
Or open the Terminal window (on Microsoft, the Command Prompt window),
go to your Python directory, and say the following.
(On Microsoft,
say
py.exe
instead of
python3.)
python3 graphpaperunittest.py
In either case, the output will be the following. The time is in seconds; running from the Terminal is faster than running from IDLE.
test_range (__main__.TestGraphpaper) Does draw raise a ValueError an argument is a non-positive integer? ... ok test_return (__main__.TestGraphpaper) Does draw return the correct value? ... ok test_type (__main__.TestGraphpaper) Does draw raise a TypeError if an argument is a non-integer? ... ok ---------------------------------------------------------------------- Ran 3 tests in 0.002s OK
If you have launched
graphpaperunittest.py
from the terminal window,
you can check the exit status of this script
immediately after running it
by saying
echo $? 0
draw
function in
graphpaper.py.
For example, change the
"+"
to
"*"
in
line
42.
The error will be discovered when the
test_return
method calls
draw
for the first time,
passing it the arguments 1, 1, 1, 1.
The hieroglyphics tell us that we’d have to remove
"+-"
from the left string and add
"*-"
to the left string to make the two strings equal.
test_range (__main__.TestGraphpaper) Does draw raise a ValueError an argument is a non-positive integer? ... ok test_return (__main__.TestGraphpaper) Does draw return the correct value? ... FAIL test_type (__main__.TestGraphpaper) Does draw raise a TypeError if an argument is a non-integer? ... ok ====================================================================== FAIL: test_return (__main__.TestGraphpaper) Does draw return the correct value? ---------------------------------------------------------------------- Traceback (most recent call last): File "graphpaperunittest.py", line 47, in test_return rowsOfSpaces, columnsOfSpaces AssertionError: '+-\n| \n' != '*-\n| \n' - +- + *- | ---------------------------------------------------------------------- Ran 3 tests in 0.001s FAILED (failures=1)
echo $? 1