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In this video, I will show
you how to 

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create a package, a class, and 
describe tests.

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The first thing to do is to 
open the system browser.

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The system browser enables to browse 
packages.

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Here there are packages.

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The first thing to do is 
to create a package. 

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We will click on “Add
package”, "MyCounter".

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As there are many packages
and we don’t want

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to see them, it is a good thing
to filter this.

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We have our package "MyCounter".

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And there, we define a class 
that we call

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"Counter" and it has an instance
variable “count”.

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The little orange icon means 
that the code has not been saved.

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Here, we will compile code
with the “Accept” function.

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And here, the class
"Counter" has been compiled.

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The system searches a little
and says that there are

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good comments. We will see this later.
For the moment, we don’t care.

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There is a red exclamation mark
because we haven’t written

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a comment.
So, we will write a first

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comment:

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"I'm a simple counter…”

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We write a little example
so that the counter understands

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how it will work:
Counter new,

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Counter increment, increment,
Counter

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count. Here it should be equal to 2.

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Once more, the text hasn’t been
saved and we will compile it.

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It has been saved. 
We don’t have a counter anymore.

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Now, we are going to define
accessors.

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We generally put accessors in the 
Accessing protocol.

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We write: "count returns count".

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In the same way, we write

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aNumber, we do a Setter.

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You see, I modified the count
method.

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You can think that it has been
lost, but no, because

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each time I change a method
using a different name, 

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it creates a new method.

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I compile the new method,
I have “count”.

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Now, we really want to test
and write our first little program.

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I open Playground.

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I create a counter,
we go on another line.

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I put a value: 

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C count 7. If I ask for its
value, what will it

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return? It will return 7.

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Now, what we’d really like
to write

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this as a test because like this
we can’t execute it

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and we’d like to execute it 
automatically.

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We create a test class.

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How do we create a test class
in Pharo?

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We change the super class,
we say it inherits this 

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from TestCase and we will
define a test class

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called CounterTest.

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Now, I will compile it.

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I have a new CounterTest class
in my system.

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I will define a new method,
I will add  

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a protocol called tests.

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There I can define a new method.

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Tests methods must always start 
by “test”

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and be in a class that inherits 
from TestCase. 

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We will call it
"testCounterisSetAndRead"

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for instance. We almost have our
test. We have already

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almost written everything.

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We will indent it a little better.

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I create my counter.

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And now, I write
"self assert

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equals 7". This sentence is

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strictly equivalent to
"self assert C count equals 7".

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It is more convenient,
when you make a mistake

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the return is smarter 
when you use the first sentence.

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We will compile. 

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Now, I can make my test executed,

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my test is green. When you have 
a test and it is green, 

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it is the right time to 
save your production, your code.

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In Pharo, you can save the image.

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Here, that’s what I do, I will 
save the image, but the image 

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is not satisfactory..

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I’d like to show you
how you can save code

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in a versions system.

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Here, as I don’t know if you will
have an Internet access,

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I will do it in my local cache. 

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You see, I have this directory
pointing toward

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all those packages
on which I can work

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and that I have loaded or not. 

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There, the system shows us that

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several packages with modifications
haven’t been saved.

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We don’t care about the first 2,
but we see that


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MyPackage has a star. It means
there is code in 

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the image that hasn’t been saved.

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Here that’s what I’m going to 
do: I click on Save,

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I choose the repository.

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I click on save.

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I write "first version 
with accessors and a

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green test".

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I accept. Now it has saved 
one package. 

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We will check.

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I can open this directory.
If I look, I contains 

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lots of packages that have been
loaded by the system.

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But in particular, if I filter,
I find 

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my package with its versions.

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I advice you to save,each time
 you add

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a feature, and that’s what 
we will do.

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Now we will define

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a test before implementing it.

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We will write a test for
what is the increment 

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of a

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counter. "TestIncrement"
What do we want to obtain?

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We want to say it “I create

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a counter,

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I assign it a default value,

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then I increment twice this counter.

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“What should I check?”

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I should check that the counter 

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has the correct value.

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I compile. My test

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is red as I didn’t implement
counter.

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The operations in counter
increment and decrement.

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I add
"operations increment".

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What will we do?

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We do "self
count 2: self count +

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1". If we use systematically
accessors  

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internally or not, it depends,
it is a question of style.

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in the same way, as it is very close,

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we will define "decrement".

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You see that on increment, there is
a test so I can 

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execute it and my test is green.

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So I do have 2 tests that work well.

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If I go in the test class, 
all my tests are green.

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What am I going to do?

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I save. I will make a new save.

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I will write "Added
increment and decrement".

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Now if I look,
I have 2 versions

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of my packages.

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We will write a test for "decrement"

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because there’s no reason 
not to do it.

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"Decrement", for instance I

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could attribute the value 2
if I want

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and I decrement twice. I should get 0.

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My test is green so

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I will save.

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Now, what we want is if I look 

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and I write "Counter new" 
and then

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"Print it", it displays a counter
which value I don’t know, 

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so it is not very useful.

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We would like to modify
this behaviour.

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To do this, we will add
a method

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called ”PrintOn",
in the Printing protocol.

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Print on is a method called

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by the system each time
you do PrintStream.

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It has aStream as an argument.

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What do we do?

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We say that we’d like 
to have a counter. 

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Here typically, I use the above
functions.

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Now what I will do,
I’d like

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to add a little

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text

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for instance 
"with value" and "self count".

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I do this because it is a
number, so I have

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to get a textual representation.

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I write "cr".

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I compile.

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The system tells me that I could do 
better, but no matter…

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For now we don’t care.

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I can write "Counter new".

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I look, it says that it is a counter 
with a nil value.

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That’s normal because I
haven’t initialised it yet.

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Now we will add a support
to the initialisation.

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To do this, we begin to write a test.

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I say: “At the creation,
I want the values

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to be 0.

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What will I do?

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I will write “self asser”

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I check that "Counter new

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count = 0". 

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There, what do we notice? 

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My test is false. Why?

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Because if I do this, 
I get nil.

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As it is a class and I don’t 
get access to

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instance variables of the 
CounterTest class, 

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I can select the expression and
execute it directly. 

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Once I have this test that isn’t
valid,

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what should I do?

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I will add an initialize method
in the initialisation protocol.

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And there what do I do?

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I write "super
initialize", and I will

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say "count 2 points = 0".

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This method is used each time
I add the “new” method.

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Now I can look at my tests,
it’s green.

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In the same way, if I write 
"count", I get 0.

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Once more, we will save:
"added printOn"

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"added initialize + tests".

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Now what is interesting is that

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I can see all my history.

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I can also see and browse this history.

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If I click on “version”, I can 
see the difference between these 2 systems.

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Changes between version 3 and version 4

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are ”initialize" "printOn" and the Test.

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If I want the difference
between

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version 2 and version 4, 

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I have all these changes.

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Now, I remains one thing to do,
I’d like

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to change a little the 
way objects are created. 

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I start off by creating 
a test that will clarify

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what I want to get.
I will define a test

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called 
"AlternateClassCreation".

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What do we want to obtain?

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Let's say, I want to 
be sure that

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that Counter withValue: 19

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If I do increment on it

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and I ask for its value,
it must return 20,

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Ok.

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Let's add a parenthesis here,
it's better.

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So, once more, the
test isn't ok,

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and the assistant tells me:
"you send an unknown message".

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You must notice that the message
withValue 

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is no more sent to an object
but to a class.

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It means I have to define this
message 

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on a class.
So I select the class.

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Now I go to class level
and I add

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a protocol called
instance creation 

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withValue: aNumber
So what do I have to do?

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The first thing to do is

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to create a counter, a counter
variable,

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counter, I do it slowly, 

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self new 
So I create a counter 

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and I write
self count: aNumber

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and I return this counter.

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We can do it in a shorter
way 

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but for the moment let's
do it simply.

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I compile my method.

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And now it means I can
send messages.

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You see, when I click on 
this button,

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I go on the class level.
I go from the class level
je passe au niveau classe.
Donc je passe du niveau classe 

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to the instance level.

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Here I was on the class level
and here I go back on

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the messages sent to 
instances.

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What does it means?
It means that if I do

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Counter withValue: 18,
what will I get?

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I will get an instance of the
counter class.

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I get a counter with
value 18.


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And here I could do
decrement.

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If I refresh, I do get 17.

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Know if I look at my test,

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all my tests are ok,
so I will once more 

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save and I'm done.

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Added instance creation 
API and tests. 

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Done for now.