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Learning code boundaries will help you spot edge cases.
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- Pragmatic Unit Testing in Java 8 by Jeff Langr
- hamcrest - an acronym for matchers is a more descriptive way to assert things. If you'd like to have a workshop on these, I'd be happy, just let me know you're interested in this powerful library.
- System Rules collection of testing rules for faking out System.
CORRECT
C - What happens when the unit receives data that doesn’t Conform to the expected format?
O - Is the Ordering of values returned in the expected order. Applications where listing results in a certain sort order is important, should definitely have tests proving that this works as intended.
R - Make sure that you check the Range. What happens if you go below the minimum or over the maximum value allowed?
R - Does this unit Reference any other code from another unit? Is that other code unit tested?
E - Remember that Existence is important in most units. Are things allowed to be null? What happens if they are?
C - You should check the different possible number of elements in a grouping, or Cardinality. Related to existence, always check what happens when there are 0. What happens with a single value, what happens with multiple values. This is often called 0-1-n, because none, one and some usually produce different expectations.
T - Remember to always take Time into account. This can be relative as well as absolute. Like for instance, sometimes applications require things to happen in a certain order. What happens if it doesn’t?
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Life sure would be easy if everything
always stayed on the happy
0:00
path, wouldn't it?
0:03
But we know, this isn't the case.
0:04
Part of the awesomeness of
unit tests is we can plan and
0:06
check on what happens when
things don't go so well.
0:09
Actually before, they don't go so well.
0:11
Now, so far, we were just kind of testing
what was already in place, surrounded
0:14
around errors that I had anticipated or
that techs had pointed out directly to us.
0:19
However, you can also use tests to
explore how things might break and
0:24
what it looks like when it does.
0:28
So, how do you find common
ways to break stuff?
0:30
Well, guess what?
0:32
I got another handy pneumonic trick
that I picked up from Jeff Landers'
0:33
awesome book "Pragmatic Unit Testing".
0:37
Now, I've found that these are hard
to think about all at once.
0:40
This little memory tool will help
you run through them quickly.
0:43
Unfortunately, we're not going to be able
to cover all of these in detail, but
0:47
we'll explore them a bit.
0:50
And I dropped a link in the Teacher's
Notes, if you want more info.
0:52
Ready?
0:55
So, when you wanna think through what
might go wrong around the edges of
0:56
the happy paths,
these are called boundary conditions.
1:00
This is where the possible
problems are usually lurking.
1:03
Try to remember the correct
way to find them.
1:06
What happens when the unit
receives data that doesn't
1:10
conform to the expected format?
1:13
Is the ordering of the values
returned in the expected order?
1:16
Applications where listing
results in a certain sort order
1:20
should definitely have tests proving
that this works as intended.
1:24
Make sure you check the range.
1:28
What happens if you go below the minimum
or over the maximum value allowed?
1:30
Does this unit reference any
other code from another unit?
1:35
Is that other code unit tested?
1:39
Remember that existence is
important in most units.
1:41
Are things allowed to be null?
1:44
What happens if they are?
1:46
You should check the different possible
number of elements in a group or
1:48
cardinality.
1:51
Related to existence, always check
what happens if there are zero.
1:53
What happens with a single value?,
what happens with multiple values?
1:57
This is often called the zero one in,
because none, one and
2:01
some usually produce
different expectations.
2:05
Remember to always take time into account.
2:09
This can be relative as well as absolute.
2:12
Like for instance, sometimes applications
require things happen in a certain order.
2:14
What happens if that doesn't?
2:19
Check the teachers notes for
more about these.
2:20
Let's go see some of these
boundary checks in action.
2:22
So, how about we write some tests for
the bins?
2:25
Now, text was pretty particular
about these should work.
2:28
Remember, he wants to make sure that you
keep the same items in the same location.
2:31
So, let's look at the bin class.
2:36
So, it looks like,
2:38
if we restock here it looks like we have
a heavy path just doing that, right?
2:39
So checks and makes sure that if
it's not empty the name equals
2:42
get item name, then, it doesn't equal it,
then it says it can't restock.
2:47
And it throws an IllegalArgumentException.
2:53
Let's make a test.
2:55
So, I want to do Command+Shift+T.
2:56
And it can't find one, so
I'm going to create one.
2:57
Let's go ahead and
leave a before in there.
3:00
And okay.
3:03
So let's go ahead and make a new bin.
3:08
Say, ten.
3:14
Right?
That's how many
3:15
items can be stored in there.
3:16
So, go ahead and create a field.
3:19
Bin.
3:23
There we go.
3:24
All right.
So,
3:25
let's make a test where we attempt
to restock with different items.
3:26
Let's do that.
3:29
So, we'll say new test,
3:30
and we will say
3:36
restockingWithDifferentItemsIsNotAllowed.
3:38
Okay, so we will first, let's stock it up.
3:48
Let's put some delicious Cheetos in there.
3:51
Was not product placement.
3:56
And then, let's also put some
delicious Doritos as well.
3:57
There.
4:04
Okay.
4:08
And let's, well obviously we know
that it throws an exception, oops.
4:09
Let's make it throw
that exception as well.
4:17
So, it was an IllegalArgumentException.
4:21
Cool, so let's run that,
make sure that's working.
4:27
Awesome, our bin test passed.
4:30
Okay, so that was using,
this Bin here was using
4:32
getItemName, which checks to
make sure that things are empty.
4:38
So, we need to be careful about that right
because the item, it might be empty.
4:43
So we need to make sure that every place
that we use that, we need to check for
4:48
cardinality.
4:51
Remember that?
4:52
Where we check for zero, one, or more?
4:53
So, we need to make sure that
anything that's looking for
4:55
information about the next item in
the bin returns the right thing.
4:57
GetItemName here is totally protected,
see how it checks for empty.
5:01
But why don't we check for what happens
if there's no items in the bin and
5:05
we check the price.
5:10
What should happen?
5:11
Let's see.
5:13
It should return zero right?
5:14
I hope so.
5:16
I mean, I know that you can buy ghosts on
Ebay, but we don't wanna be charging for
5:17
nothing, so let's add that edge case.
5:21
So, let's flip back to the test.
5:23
Let's add that edge case for
what happens when it's zero.
5:25
Let's make sure.
5:29
Let me say when empty price is zero.
5:32
So, we'll just go ahead and
because it's going to start out empty, so
5:38
say zero bin get it Item price.
5:42
Let's see what happens.
5:45
That should happen, right?
5:46
Testing this edge case here, oh!
5:48
We got one!
5:51
I mean, well we found one,
that's not a good thing, but it's good for
5:53
what we're doing right now because
we're gonna fix this, right?
5:56
So, let's go back to our bin class here,
and let's take a look and
5:59
see why is it returning
a null pointer exception.
6:02
Oh!
6:05
Because it's just doing a peak in the peak
here is it's chain is gonna return a null,
6:06
and if you call get retail price a null,
Null pointer exception.
6:11
We don't want that.
6:16
So, let's go ahead and what should we do?
6:17
It should return 0, right?
6:19
So, let's just fix the code
here to make the test pass.
6:20
So, say if is empty,
let's return 0, right?
6:23
We can do that,
we can return 0 in the middle of a, oops.
6:28
And then, if it's not empty, obviously,
6:33
there's 1 in there it can get
the retail price of what's there.
6:36
Let's go ahead and run that.
6:38
All right, our test passed, good job.
6:40
You know what?
6:42
I saw in there.
6:43
Let's make sure that
this never gets broken,
6:44
that nobody thinks that this
line should just go away.
6:46
So, let's go ahead and
add the test for that.
6:48
Again, that's pretty easy.
6:51
New test method, and let's say
6:53
whenEmptyNameIsNull, little
probably more specific.
6:57
Maybe we could word that better,
but let's make a new test.
7:02
So, let's use this assertion,
there's a lot of assertions on here and
7:06
we haven't really played
with too many of them.
7:09
Let's do assert, no.
7:10
Oh, look at that, there's one in here for
that, exactly what we want, and
7:12
it just takes the object or
a message in the object like we saw, so
7:15
we'll just pass and get item name, right?
7:19
So, that should make sure that, that's
pretty explanatory in what it's doing.
7:21
Bam!
7:26
Awesome.
7:27
Here we've used another assertion
in the awesome assert class.
7:28
There are a ton here, and there is an even
more expressive language that is outside
7:31
the scope of this class called Hamcrest,
which is an anagram for matchers,
7:36
where you can match on
these different things.
7:41
Check the teacher's notes below for
7:43
more info on these powerful
descriptive assertions.
7:44
So, let's try the boundary
check surround range.
7:47
Remember, the second R
in the correct pattern.
7:50
So, range-wise,
we know that there's a top limit, right?
7:53
It's ten.
7:56
I know that there should be code
in place to stop overstocking.
7:57
Well, why don't we just rock
out a test really quick and
8:00
see what happens when we overstock?
8:02
Because it's faster just
to write the test, right?
8:07
So, let's just say over stocking
not allowed, see what happens.
8:10
So, we'll do a restock delicious Fritos,
I'm getting hungry,
8:17
twenty six hundred,
one hundred, and fifty.
8:22
Okay, so let's run that.
8:27
Oh, that's a very
descriptive error message.
8:32
It's dynamic,
it says there's only 10 spots left.
8:34
That would be nice to test, wouldn't it?
8:37
Since we're taking the time to
make such a dynamic message,
8:40
we want to make sure that the message
actually says what we want it to.
8:42
The current way that
we're testing exceptions,
8:45
we just use the expected value
in the at test annotation.
8:47
Well, there's a pretty powerful
tool in j unit called rules.
8:50
Let's touch on them here briefly and then,
8:55
I'll show you in the notes
where to learn more about them.
8:56
So, rule allow you to redefine
behavior in each test method.
8:59
There is one to do exactly
what we're talking about here.
9:04
If you wanna access the exception
thrown inside your test and
9:07
still ensure it's thrown,
you wanna define a rule.
9:11
So, what you do is make a rule with
a rule annotation just like this.
9:14
We say @Rule.
9:17
Public.
9:23
And we're looking for
ExpectedException is the name of the rule.
9:25
And we're gonna name it thrown.
9:30
You can name this whatever you want.
9:31
And by default we want it
always to be none, right?
9:34
We don't want the exceptions to be
thrown unless we specifically say so.
9:38
So, in here, in our test, in this
overstocking, we want to arrange and
9:42
we wanna say that thrown.expect, and
we expect right down here, right?
9:48
Let me get that out of the way.
9:54
We expect illegal argument
exception to be thrown.
9:56
Illegal argument exception class.
10:00
And then, we also want to
specifically expect the message.
10:03
Expect that there are only ten spots left.
10:10
So, grab that.
10:15
Put it here.
10:16
Here we go, I'm gonna run it.
10:19
And boom, it passes.
10:23
And note that it doesn't have
the expected appearance inside
10:24
here is where we're using the rule.
10:27
It's pretty powerful, right?
10:29
Now we're making sure that with the value
goes out of range that we catch the error
10:31
and that the dynamic message
provided is correct.
10:35
So, let's take a look again at
our alpha numeric chooser test.
10:39
So, let's alpha numeric chooser test.
10:42
There we go.
10:45
Our choosing wrong input test here is
a great example of a conformance test.
10:45
The C, right?
10:50
We have another range test on choosing
larger than max columns is not allowed.
10:52
Hey, let's check the range of what
happens when we use more rows
10:56
than there are letters in the English
alphabet, which is 26 right?
10:59
So, we'll make
11:03
constructingLargerThanAlphabetNotAllowed.
11:08
So, we'll just make a new
alphanumeric chooser, 27, yeah.
11:17
We'll go ahead and run that.
11:26
Ooh, maximum rows supported is 26,
so again it's a dynamic message.
11:30
Why didn't we catch that?
11:35
Actually, why don't I put that
on your plate to catch and
11:36
verify that we get the message correctly.
11:39
Boundaries are super helpful
when your trying to find out
11:41
how your code might break and they're
especially helpful when considering
11:44
when writing tests first by
using test driven development.
11:48
Now, we had already done a pretty
good job of thinking through
11:51
plenty of possible bugs but the boundaries
will help you think through even more.
11:53
There's tons of good stuff
in the teacher's notes.
11:58
Glad you got a change to play around a bit
with rules, they are super powerful and
12:01
you can also write your own.
12:04
There's actually third party
rules that you can use.
12:06
Someone wrote one that lets
you fake out the input and
12:09
capture the output from
a console based program.
12:12
Speaking of faking, one of the important
pieces of test that we haven't covered yet
12:16
was mentioned in both of our acronyms.
12:20
First and correct.
12:22
The I is isolated and
the second R reference.
12:24
So, how do we make sure that
our tests are isolated?
12:28
The answer, my friend is test doubles.
12:31
And it's part of a larger discussion
which is what should we not test.
12:34
Let's go learn about what not
to test right after this break.
12:38
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