lab02 : More practice with writing functions and test cases

num ready? description assigned due
lab02 true More practice with writing functions and test cases Tue 04/10 12:30PM Fri 04/20 05:00PM

In this lab, you’ll get more practice with:

This lab may be done solo, or in pairs.

Before you begin working on the lab, please decide if you will work solo or with a partner.

If you decide to work with a partner:

The following arrangement is NOT OK.

This is NOT how pair programming is done!

There are a few requirements you must follow if you decide to work with a partner:

Once you and your partner are in agreement, choose an initial driver and navigator, and have the driver log into their account.

Step 1: Verify that pytest is working on the machine you plan to work on

Similar to lab01, you can check whether pytest is installed by typing in the following command in the Python shell prompt. If it returns no error message, then pytest is installed. If you get an error, refer back to lab01 for instructions on installing it.

If you are working on CSIL, that works like this:

[cgaucho@csil-12 ~]$ python3
Python 3.4.3 (default, Aug 9 2016, 15:36:17) [GCC 5.3.1 20160406 (Red Hat 5.3.1-6)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import pytest
>>>

On your own machine, you might need to type python rather than python3 but be sure that the version of Python running is some version of Python 3.

Step 2: Make a ~/cs8/lab02 folder.

The easiest way to create this is to do the following, which will work from any directory:

mkdir -p ~/cs8/lab02

That form of the mkdir command, with the -p has the advantage that

Then, to get yourself into that directory, type:

cd ~/cs8/lab02

Again, since that’s an absolute path, it works from any directory.

Step 3: Create a file called lab02.py in your ~/cs8/lab02 directory

To start out lab02, write the line:

import pytest

Then, copy this function definition into your lab02.py file.

def perimRect(length,width):
   """ Compute perimeter of a rectangle """
   return -42.0 # stub  @@@ replace this stub with the correct code @@@

Then, copy these function definitions into your file. These are a special kind of function called a test case. These particular test cases are written in the style used by the pytest testing framework, and they follow these rules:

  1. The name of each test cases function must start with test_.
  2. Each one ends (typically) with a line of code that starts with the keyword assert, followed by a boolean expression.
    • If the expression is True, the test case passes
    • If the expression if False, the test case fails
  3. Each test case function must have a different name (hence: test_perimRect_1, test_perimRect_2, test_perimRect_3, etc.) They don’t have to be consecutive numbers—we could use _a, _b, _c or anything really, as long as they are all different. In general though, your parameter, variable, and function names should be descriptive for better readability.
def test_perimRect_1():
   assert perimRect(4,5)==18

def test_perimRect_2():
   assert perimRect(7,3)==20

def test_perimRect_3():
   assert perimRect(2.1,4.3)==pytest.approx(12.8)

Finally, run the code, and ensure that you don’t have any syntax errors in your Python code.

Step 4: Test your code by hand

Because we want to be sure that you continue to practice the skill, test your code by hand first.

That is, select “Run Module” in IDLE, and then type in a few function calls at the Python Shell Prompt. Here are a few:

>>> perimRect(4,5)
-42.0
>>> perimRect(7,3)
-42.0
>>>

Ok, so that’s sort of pointless as long as we haven’t fixed the function yet. The point is that

There is a reason for that. We call this a “stub value”. It returns the wrong answer on purpose so that we can check that all of the tests fail. We want to see all of the tests fail, THEN see all of the tests pass. That’s the general idea.

Step 5: Run pytest on the file so far

As a reminder, you run pytest OUTSIDE of idle, at the regular terminal prompt.

You may find it helpful to bring up a second terminal window and use

cd ~/cs8/lab02

to get into the correct directory. Then use:

python3 -m pytest lab02.py

You should see three test failures. If you do, then you ready to fix the code so that it works, which is the next step.

(If you need a refresher on how to interpret the output of pytest, refer back to lab01)

Step 6: Fixing the code for perimRect

So, if you have failing test cases, the thing to do is fix the code so that the test cases pass.

Of course the formula for the perimiter of a rectangle with length and width is, in math notation: . But you’ll have to convert that into Python, and use the variables length and width to get it to work properly.

Once you have the code correct, try testing both using interactive testing as well as by running pytest.

You are by no means finished with this lab. But, we want to encourage you to make a submission to Gradescope now anyway. Here is why:

  1. After you upload your file (and this must be done each time someone uploads a file), you must add your partner (if you’re working with one) on Gradescope by selecting “Group Members” -> “Add Member” and selecting your partner from the list.

  2. It will be a way that you can share your work in progress with your pair partner. Both of you will be able to login to Gradescope and access the file(s) you uploaded.

  3. It provides a backup copy of your work in case something goes wrong with your computer (yes, this happens and you want to make sure there is a backup somewhere).

  4. It provides a staging ground for you to move your file between you and your partner.

  5. You also will be able to see some progress towards completion of the lab— partial credit for completion of this step.

Once you’ve submitted and you see that you have 20/60 points, you are ready to continue with the rest of the lab.

Step 7: Write a areaTriangle function and test cases.

You will write your own function areaTriangle(base, height) and some test cases in your lab02.py file. Be sure you define your function’s signature with the exact name shown here. It’s also a good habit to define comments for all the functions you write. Include a comment for areaTriangle to describe what this function does. Note that the function comments have to either be in a string (as explained in the textbook), enclosed in triple single-quotes, or enclosed in triple double-quotes (as shown in the perimRect function). Your function should return the area of a triangle using the base and height parameter values.

You should try to make the function pass the test cases that you put in.

In some cases you’ll be given the test cases. In other cases, you have to supply these test cases yourself.

At each step, you should first try to get the test cases to pass by running pytest at the Unix command line as discussed above.

Once you see your tests are passing, THEN submit a version to Gradescope to see if you also pass the test cases the instructor defined in Gradescope.

If you pass your own tests, but NOT the instructor supplied tests, then try to see if you can figure out why. Are there some cases that you did not consider?

In this step, you must define three test cases to test areaTriangle. The code for the first test case looks like this

def test_areaTriangle_1():
	assert areaTriangle(4,5) == 10

The second and third test case should be one that you come up with yourself. The restrictions are:

Once this is done, then:

Once everything passes correctly with pytest, submit your lab02.py file to Gradescope again to see if your submission passes the areaTriangle tests. You should see that you now have 100/100 points if all the tests for perimRect and areaTriangle pass.

Remember to add your partner to Group Members for this submission on Gradescope if applicable.

Step 10: Uploading your files to Gradescope

Navigate to the Lab assignment lab02 on Gradescope and upload your lab02.py and lab02_face.py.

Your Gradescope submission will be autograded out of 100 points.