chapter-11.srt

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Chapter 11.
Specifying Target behaviour
with older and newer dependencies.

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JC: OK, now everything is passing,
so the thing does check its mtime.

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The next question is does it use the mtime
to do something useful like skipping work.

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So when the dependencies are newer than the target...

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And that means... So let's say...
Some offset to base these on...

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Let the target_time be Time.now.

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And then we can say, use that here.

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And then it's clearer that they are in
the future from when the target was built.

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It doesn't matter that it's Time.now

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TS: So are you using Time.now as the most
convenient way to get a real time value?

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JC: Yes, actually the current time is not relevant.

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So what's the context? When the
dependencies are newer than the target.

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That means that the...

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allow(File).to receive(:mtime)

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So the time the target asks
for will return the target time.

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And we need exists to return true as well.

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The target will use target_time as its time and the
dependencies have times which are later than that.

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The dependencies are newer, so that means
the target should execute its instruction.

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But we haven't given it any instructions.

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[Silence]

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Let the instruction be echo something;
it doesn't really matter what it is.

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System is stubbed out in all these tests,
so I'm not really worried about that.

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And also we want that output here because
it's going to start printing stuff otherwise.

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Do we have that everywhere? We do, OK.

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And that line's got quite long so
I'll use terminator block like that.

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So we have a target with some dependencies,
an instruction and an output stream.

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So we want to say is that in
this case it executes its instruction.

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I don't want to specify this by saying you should
invoke some private method that you have,

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because that's over specifying
the implementation.

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I want to specify the effect that it has on the
world which is that it makes a system command.

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So, we expect the target to receive system
with the instruction once when we build it.

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Now, it will prob do this anyway
because it isn't checking anything so far

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because I haven't introduced
anything that will make that test fail.

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TS: So you're currently testing
what it would already do.

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But what we're driving towards is what happens when
it's NOT out of date, and you haven't tested that yet.

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JC: Exactly.

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JC: It's basically going to result
in duplicating most of this context.

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So I feel I should pull some of this stuff out.

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Lazy building.

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So if i have that... I want to take this stuff
which is going to be needed for all of these tests,

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and put it in here. But not like that!

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And then...

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[Silence]

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Is that all back in shape? I think so... Yes.

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TS: So what's going to be
different in the other context?

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JC: The difference is these steps here,
rather than returning things in the future

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will return things in the past; or the past
relative to the targets' own modification time.

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And in that case we shouldn't execute
the instruction, but just leave things alone.

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So I'm going to copy most of that.

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and they are not newer, they are older.

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And these can be minus signs.

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And we can say it does not execute its instruction.

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And this is the thing that should fail.

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[Silence]

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So target.system("echo hi")
expected zero times; received one time.

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So that's the thing that needs fixing.