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-Hello, everyone.

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In this video, we will be looking
at how to create a test class

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and some tests within it.

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In the last part, we tried to see
if our accessors were working correctly.

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Right now, we want to replicate
this behavior within a test.

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In order to do that,
let's just go to the counter class

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and create "CounterTest",

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that will be a subclass
not of objects but of test cases.

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And we will not need
the "count" instance variable.

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Now we can press Cmd+S.

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The CounterTest has appeared.

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You can see that there is a grey button
on the left side.

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This grey button can be used
to run over tests within the class.

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Right now, there are no tests
so it is not doing much.

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But we will just create one
that we will call :

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"testCounterisSetAndRead".

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Let's just copy and paste
the code right here

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and on the last line,
so the last expression,

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we will not simply output
the value of an instance variable

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but run it against 7
and see if it is correct.

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In order to do so,

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we can just write "self assert",

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then "c count"

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and we want to run this
against "equals 7".

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This will try "c count"
and see if it is equal to 7,

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which is what would set it up to,
so it should work.

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Let's press Cmd+S.

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Our method is created
and we can see that,

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the same way there is a grey button
at the side of the name of the class,

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there is a grey button there,

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so this will run the test
for this method.

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If we click on it, we can see
that it ran and it passed.

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If we click on this button there,

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it will run all tests
from within the class.

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It will only run one for now.

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When your tests are green,

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it is a good time to save your image.

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We can go to the menu, Pharo, Save.

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Now, let's create another test
but with another mindset.

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Let's try to do
some test-driven development.

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What that means is
that we will write the test first,

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and implement the method
it needs to be green.

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We will just try
to make a test increment.

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We will set the counter to 4,

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then increment twice

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so we can do with a semicolon.

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"Increment; Increment".

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And we want it to be equal to 4
and let's put this one too.

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Okay.

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This should add 2 to the counter.

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Let's compile it.

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We can see that the method has appeared.

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But if we click on the button there,

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it should fail because we did not define
the increment method,

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so let's click on it.

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Yes. "Instance of counter
did not understand increment".

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That's right, we have to define it,
so let's go back to the counter class.

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Let's go here

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and create a new method
called "Increment"

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that we want to add 1 to the count.

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Capitalize that.

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"Count + 1".

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Let's compile it, Cmd+S,

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and you can see that the button is now
on the left of the name of the method,

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first because the system knows

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that there is a test
called "testincrement"

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that is linked to this method.

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We can just click on this one
and now, it's green.

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If you go to our CounterTest
and press the button,

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it is now running two tests
and the two have passed,

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so it is a good time
to save our image once again.

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Save.

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The same way we defined increments,

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we will go and define a test decrement.

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It will run the same method.

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"Decrement; Decrement",
but now we want the count to be 0

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because we subtract 1 twice.

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If we compile, Cmd+S,
the method appears

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and if we run it,
it should fail and it is failing

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because it does not understand
"decrement"

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because we did not define it,
so it is perfectly normal.

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Let's just go back to the counter class
and define "decrement"

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so it should subtract 1 this time.

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Once again,

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it recognizes that there is a test
associated to this method

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with the button to the left.

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We can just click on this one,
it is green,

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and now, if we click on the CounterTest,

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it just runs all the tests
from within it.

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We can see 3 tests have been run,
3 passed.

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It is a good time to save the image.

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In this video,
we learned how to create a class test

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and how to define some methods.

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Once again, test-driven development
is encouraged from within Pharo

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as it is really simple to write tests

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and you will see in the next week
how it is even easier to define methods

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such as the methods decrement
and increment that we just wrote.