functions 3

Since I know how to use for loops, I can do better with the assertions of test_why_use_a_function

open the project

I change directory to the functions folder
```
cd functions
```
the terminal shows I am in the functions folder
```
.../pumping_python/functions
```

I use pytest-watcher to run the tests

uv run pytest-watcher . --now

the terminal shows

rootdir: .../pumping_python/functions
configfile: pyproject.toml
collected 12 items

tests/test_functions.py ............                          [100%]

======================= 12 passed in X.YZs =========================

I hold ctrl on the keyboard, then click on tests/test_functions.py to open it in the editor

a better way to test why use a function

RED: make it fail

I add a variable to test_why_use_a_function

    def test_why_use_a_function(self):
        def add(x=3, y=0):
            return x + y

        x = 4
        numbers = (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)

        y = 0
        self.assertEqual(add(x, y), x+y)

I add a for loop with an assertion and the subTest method

        x = 4
        numbers = (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
        for y in numbers:
            with self.subTest(y=y):
                self.assertEqual(add(x, y), x+x)

        y = 0
        self.assertEqual(add(x, y), x+y)

the terminal shows AssertionError

SUBFAILED(y=0) ... - AssertionError: 4 != 104
SUBFAILED(y=1) ... - AssertionError: 5 != 104
SUBFAILED(y=2) ... - AssertionError: 6 != 104
SUBFAILED(y=3) ... - AssertionError: 7 != 104
SUBFAILED(y=4) ... - AssertionError: 8 != 104
SUBFAILED(y=5) ... - AssertionError: 9 != 104
SUBFAILED(y=6) ... - AssertionError: 10 != 104
SUBFAILED(y=7) ... - AssertionError: 11 != 104
SUBFAILED(y=8) ... - AssertionError: 12 != 104
SUBFAILED(y=9) ... - AssertionError: 13 != 104

GREEN: make it pass

I change the calculation to x+y

          x = 4
          numbers = (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
          for y in numbers:
              with self.subTest(y=y):
                  self.assertEqual(add(x, y), x+y)

the test passes

REFACTOR: make it better

I remove the other assertions because the for loop does what they do

      def test_why_use_a_function(self):
          def add(x=3, y=0):
              return x + y

          x = 4
          numbers = (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
          for y in numbers:
              with self.subTest(y=y):
                  self.assertEqual(add(x, y), x+y)

      def test_making_a_function_w_pass(self):

I add a for loop for the value of x

          x = 4
          numbers = (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
          for y in numbers:
              for x in numbers:
                  with self.subTest(x=x, y=y):
                      self.assertEqual(add(x, y), x+100)

the terminal shows AssertionError

================== 100 failed, 12 passed in X.YZs ===================

the two for loops go through every combination of x and y

(x, y)
(0, 0)
(0, 1)
(0, 2)
...
(5, 0)
(5, 1)
(5, 2)
...
(9, 7)
(9, 8)
(9, 9)

I change the calculation in the expectation to the right thing

                    self.assertEqual(add(x, y), x+y)

the test passes

I remove the x variable, then the default values from the add function

    def test_why_use_a_function(self):
        def add(x, y):
            return x + y

        numbers = (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
        for y in numbers:
            for x in numbers:
                with self.subTest(x=x, y=y):
                    self.assertEqual(add(x, y), x+y)

the test is still green

I can use a list comprehension instead of the 2 for loops

        numbers = (0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
        for y in numbers:
            for x in numbers:
                with self.subTest(x=x, y=y):
                    self.assertEqual(add(x, y), x+y)

        for x, y in ((x, y) for x in numbers for y in numbers):
            with self.subTest(x=x, y=y):
                self.assertEqual(add(x, y), x+100)

the terminal shows AssertionError

================== 100 failed, 12 passed in X.YZs ===================

I change the calculation in the expectation
```
15                self.assertEqual(add(x, y), x+y)
```
the test passes. That used for 3 times, confusing.

I can do the same thing with the product method from the itertools module which comes with Python, it needs an import statement

        for x, y in ((x, y) for x in numbers for y in numbers):
            with self.subTest(x=x, y=y):
                self.assertEqual(add(x, y), x+y)

        import itertools
        for x, y in itertools.product(numbers, repeat=2):
            with self.subTest(x=x, y=y):
                self.assertEqual(add(x, y), x+100)

the terminal shows AssertionError

================== 100 failed, 12 passed in X.YZs ===================

I change the expectation

                self.assertEqual(add(x, y), x+y)

    def test_making_a_function_w_pass(self):

the test passes, not as confusing.

I can use a range object to make the test use more than 10 numbers

        # numbers = range(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
        numbers = range(-10, 10)
        for y in numbers:

the test is still green

I change the expectation in the first assertion

        # numbers = range(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)
        numbers = range(-10, 10)
        for y in numbers:
            for x in numbers:
                with self.subTest(x=x, y=y):
                    self.assertEqual(add(x, y), x+100)

the terminal shows AssertionError

================== 400 failed, 12 passed in X.YZs ===================

the test takes longer to run because there are more numbers to calculate

I change the expectation back then remove the commented line

class TestFunctions(unittest.TestCase):

    def test_why_use_a_function(self):
        def add(x, y):
            return x + y

        numbers = range(-10, 10)
        for y in numbers:
            for x in numbers:
                with self.subTest(x=x, y=y):
                    self.assertEqual(add(x, y), x+y)

        for x, y in ((x, y) for x in numbers for y in numbers):
            with self.subTest(x=x, y=y):
                self.assertEqual(add(x, y), x+y)

        import itertools
        for x, y in itertools.product(numbers, repeat=2):
            with self.subTest(x=x, y=y):
                self.assertEqual(add(x, y), x+y)

    def test_making_a_function_w_pass(self):

the test is green again

I can use a for loop to remove duplication

close the project

I close test_functions.py and functions.py in the editor
I click in the terminal, then use q on the keyboard to leave the tests. The terminal goes back to the command line
I change directory to the parent of functions
```
cd ..
```
the terminal shows
```
.../pumping_python
```
I am back in the pumping_python directory

review

I used a for loop to remove repetition.

Why did my “list comprehensions” look like tuples and not lists?

code from the chapter

Do you want to see all the CODE I typed in this chapter?

what is next?

you know

Would you like to test dictionaries?

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