CSCA08 Winter Week 12: Exceptions & Testing. Marzieh Ahmadzadeh, Brian Harrington University of Toronto Scarborough

Transcription

1 CSCA08 Winter 2018 Week 12: Exceptions & Testing Marzieh Ahmadzadeh, Brian Harrington University of Toronto Scarborough

2 Administrative stuff We ll have a surprise for you: An extra exercise! You don t have to do it however for better learning I strongly recommend you to do it. This helps to drop one of the exercises in which you received less mark. Deadline does not follow our regular date & time April 6 th 2

3 Exceptions By now you ve probably received all types of errors: Syntax, Runtime, Logical And you ve probably were able to handle it. But there are some situations that cannot be easily handled by programmers: e.g. You are using a file that is deleted by another user. Your code will crash anyway, But instead of receiving python s error message, you want to receive your own tailored error message. In this case, you throw an exception 3

4 Try/exception try: block of risky code exception ExceptionType: a block of the code, which is run if ExceptionType happens. you can handle more than one exception: This is a default exception. Must be your final exception else: If no exception exists, this code will be run finally: this code will be run regardless of having an error or not! 4

5 Making your own exception Need to create your own exception object. Exception is a built-in data type. Your exception should extend python s Exception. When you came across the exception, you raise your own exception. This is beneficial to avoid revealing your implementation detail in case an error happens. A solution to leaky abstraction Before throwing an exception: Think about it: Can you handle it such that your code does not crash? e.g. in case user input is required you can verify the type and value before proceeding to the next level. 5

6 Black Box Testing Functionality is tested You don t need to know how a function is implemented. All you need to know is for some certain data, what is expected as an output. It is not possible to test all possible inputs. You need to test the inputs from all major areas You need to test the boundary cases. The tester is not necessary part of programming team! 6

7 White Box Testing Is mostly focused on implementation details Goal is to test all the paths, if possible, in the code. Still we focus on what should be the output if certain path is followed. This test is done by programmers. 7

8 Unit Test Can be used for all type of testing. Normally it is automated. A unit can be a function ( in functional programming) or a class ( in OOP). Python provides DocTest Useful for testing the functions Not very useful, for dictionaries and sets, if possible at all Not good for testing classes 8

9 DocTest import unittest import your file name in which there are functions that you want to test you can choose an alias for your file name Write a class that extends unittest.testcase for each function. Write one method for each test case. Name should start with test. Call your function inside the method and record the returning result. Record the expected return value. Use assertequal to check for the equality of returned result and expected result. There are other assert functions that you can use such as asserttrue. 9

10 Regression Testing Change a unit of your code, you need to test other units that used this unit. It is possible that by improving this unit, you have introduced new bug for other units. It is costly but very effective. 10

11 Adversarial Testing Tries to break the code by inputting what is not expected. This will tell you where you need to patch/correct your code. You find new bugs. 11

12 Testing Type Black Box White Box Regression Adversarial Your test case should cover all possible groups of data. Test with a representative from all the groups. Don t forget the boundaries. e.g. if ( x < a): if ( y > b ): S1 elif ( y == b): S2 else: S3 else: if ( y > b ): S1 elif ( y == b): S2 else: S3 Level Unit Integration System Acceptance Release alpha beta full-release 12