#100DaysOfCode in Python Transcripts
Chapter: Days 10-12: Testing your code with pytest
Lecture: Mocking user input and exceptions
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The second thing I want to test is the guess method.
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It takes a user input and input is not static,
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you can change and it can be random.
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Even worse, when you run this program
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it's waiting at the prompt to get input
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so your test would hang, quickly demo this.
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Let's make a game object, and run it.
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Actually it's not hanging, it's throwing an error,
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pretty soon, reading from standard input
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output is captured, so that's cool.
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And look at the output, it's pretty verbose
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which is a nice feature of pytest.
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But anyway, we definitely don't want to use input
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literally in tests, so I'm going to use patch again.
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And I'm going to patch the built-ins input,
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and this is another way of marking.
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Here I can give it side effects.
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And a list of expected returns in a row.
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Because I'm having all these exceptions here,
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I'm going to give it a bunch of inputs
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to go through all these scenarios and see
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if each scenario throws the value error
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or accepts the guess as a correct one.
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And will also show you how you can check for
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exceptions in pytest which are important
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because raising exceptions is a common Python pattern.
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So what we're doing here is setting up
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a sequence of return values as if input was
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called that many times.
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So it will return a 11, then 12 as a string,
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then bob, then 12,
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then five minus one, 21
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seven and None.
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And those are the values that we're going to work with,
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and you have to give it an argument,
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it can be called anything.
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And now we have some return data from input to work with.
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So I'm making a game, and again,
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the constructor sets defaults
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for all the internal variables,
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so that should be fine,
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and then I can start to make assertions.
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And the first two side effects or returns are good.
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and again I will show you guess,
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so guess goes through getting an input,
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looking for all the bad inputs and raise a value error
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if so, and if it's good it ends up adding
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it to it's internal set which is the underscore guesses,
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and returning the guess.
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So 11 is good,
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12 is a string should be fine
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because that can be converted into a int.
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The second one, bob, is not a number.
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And the way in pytest to check if an exception is raised
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is to use pytest, and you need to import that,
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and do a with pytest.raises,
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the name of the exception and then the statement
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that would trigger that exception.
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So the next return value from input in the row
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is bob's string, if I call guess with that
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it should raise a value error
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and we're telling pytest to check if
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it actually raises that exception.
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And the same is true for the next one with is 12.
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If I guess again, the guess is already in the guesses set
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and the function manually raises a value error.
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I can just copy this and it will be the same.
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So every new call of guess triggers this input statement
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or call, which triggers a new value in the return list.
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So 12 is done, five should be fine.
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Right let's run what we have so far
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because it's a lot of code and see if it works.
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All right that looks good.
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So now let's do the complete list again.
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And after five comes minus one and 21
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which should be two exceptions because
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they are out of range.
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Another good one, and finally None should not be a good one,
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that falls into this one, if not guess
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raise a value error, please enter a number.
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So we wrap up with...
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So that's save, Control + Z, pytest
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you're still happy.
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I mean if it would say...
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Game guess returns None when given None it will fail.
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So we have please enter a number
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so it actually raised a value error,
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and it was not catching that.
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Here I do, and it works.
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So that's how I use mocking to circumvent
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this input function waiting for input.
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I'm going through all these scenarios
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by giving various side effects.
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Next up, validate guess.
