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Most of the power of testing in Python comes from the `unittest` framework and it's `TestCase` class. Let's look at starting a `TestCase` and writing a couple of simple tests.
New Terms
unittest - Python's library for writing tests
TestCase - A collection of tests
Running tests
Command line
python -m unittest tests.py
In a script
unittest.main()
Remember, all tests in a TestCase have to start with the word test_ to be run. You can have methods that don't start with test_ for other purposes if you need them.
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All the code that we need for writing unit
tests is included in the Python
0:00
standard library, in a module named Unit
Test.
0:03
We'll need to import it in each of our
test files.
0:06
The main structure that we're going to be
creating is called a test case.
0:09
A test case is a class that contains
multiple methods, some of which are tests,
0:12
and others that are just methods that you
need.
0:16
There are two special methods, Set Up and
Tear Down, that are run before and
0:18
after each test.
0:21
But we'll look at those while we write our
tests.
0:23
Speaking of, let's get to that right now.
0:25
Once upon a time, I gave the Treehouse
Forums a challenge.
0:28
I wanted everyone to build a
Rock-Paper-Scissors style game,
0:32
where you'd have three things or more.
0:37
Each one is better and worse than some of
the others.
0:40
As a player, you get to pick one of them,
and the computer would pick one.
0:44
And then we, we see, okay,
0:48
the one that you picked is better than the
one the computer picked, or vice versa.
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And so, eventually you'd win, or you'd
lose, or you'd tie.
0:53
So this inside the rps folder here, this
is my version of the game.
0:56
And the game itself, the part where you
pick the moves and everything like that,
1:01
is a little tricky to test just by the
basics of unit test.
1:06
You need to know some stuff that we're not
gonna actually cover in this course to be
1:11
able to test this one easily, and there's
probably also some clean up and
1:15
refactoring I could do to make it easier
for that,
1:20
but we're not gonna worry about it.
1:22
What is good, though, for testing, is this
moves.py file.
1:24
So, moves.py is the different moves you
can take.
1:29
You can take a rock.
1:32
You can take paper.
1:32
You can take scissors.
1:33
And, this covers how they interact with
each other.
1:34
So, we're not quite ready to test this
yet.
1:38
That's probably gonna be the next video.
1:40
We don't know about unit tests, because we
haven't written any unit tests.
1:43
So, let's actually write our first set of
unit tests, and
1:46
then we'll be well on our way to being
able to do this.
1:50
So we'll get a new file.
1:53
And I'm gonna call this test.py, and what
do I need to do in here?
1:54
Well, first thing you need to do is bring
in the unit test library,
2:00
because that's what let's me write tests.
2:04
So, import unittest.
2:06
And then, since I want to test all the
stuff here at moves.py,
2:10
let's just import moves.
2:14
Okay, so we're cool, we're good.
2:17
Now, unlike doc tests, we're gonna write
all of our tests in a separate file,
2:19
we're not gonna write our tests in the
file with our actual running code.
2:23
To write our tests, we're gonna group our
tests into what's called a test case.
2:27
So, we're gonna make a new class and we're
gonna call this MoveTests, and
2:34
it's going to extend unittest.TestCase.
2:39
Now, it's not required that you put the
word tests into the name of the class for
2:43
your test case.
2:48
It's pretty common practice, and it kind
of denotes, hey, these are the tests for
2:49
this thing.
2:52
But there is one naming convention we have
to follow, and
2:53
that is that our tests have to start with
the word test.
2:57
So, we'll say def, cuz we're defining a
function, or rather, a method, and
3:02
test, and just to get to grips with how
unit test works,
3:07
let's write two simple tests that are all
about math.
3:12
So first, let's do five plus five.
3:15
Okay?
3:21
So, 5 plus 5 is 10.
3:22
Let's make sure that's true.
3:22
We're gonna use the assert keyword,
3:24
which says make sure that whatever comes
after me is true.
3:26
So, 5 plus 5 is equal to 10.
3:30
Okay?
3:33
Easy enough.
3:34
We know that's true.
3:35
Let's write one more.
3:37
We'll do one plus one, which also extends
self.
3:37
And let's assert, all right one plus one
equals three is not true.
3:41
[BLANK_AUDIO]
3:46
Right, assert not, so that's a swap.
3:50
This is gonna come back as false, the not
swaps it over to be true,
3:53
and the assert goes hey, it's true, cool,
I'm happy, okay?
3:59
So, let's try running this.
4:03
Let's see what we can do.
4:05
So, I'm going to go into the rps
directory, and
4:07
I'm gonna do python -m unittest tests.py.
4:12
So, just like when we ran doc tests, we
specify the -m module for
4:17
unit test, it knows how to find and run
the tests.
4:22
It ran two tests, we got two little dots.
4:27
It took it basically no time at all, and
everything's okay, everything passed.
4:29
Great.
4:34
That's amazing.
4:35
Lots of times, though, so, I, I mentioned
with doc tests,
4:36
I don't usually want to run them every
time I run the script, which is true.
4:39
With unit test, though, I kinda wanna just
be able to run tests.py, and
4:43
it'll run the unit test for me.
4:47
So, let's go add that in.
4:49
We go down here to the bottom.
4:51
[SOUND] And we'll add if
4:53
name is equal to main,
4:57
unittest.main.
5:02
So, what this does is, if we run the file
directly,
5:06
run the unit tests that are in here.
5:09
Now, let's try that out.
5:11
But you should be able to do python
tests.py, and we get the same output.
5:13
Starting a test case is pretty
straightforward, and
5:18
it's really handy being able to run the
tests through either the -m
5:20
argument to our Python command, or with
that if name equals main pattern.
5:23
The test that we wrote all used the word
assert, and
5:28
a statement that we expected to be true.
5:30
This works, but isn't always the most
convenient way to word a test.
5:32
In the next stage we'll look at several of
the available assertions or
5:36
testable conditions that test case gives
us.
5:38
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