I am facing some difficulties in understanding test harness and related common terms like test case, test scripts in automation testing.
So this is what I got so far: Automation testing is the use of a special software (other than the software being tested) to control the execution of tests and compare the actual results with the expected results. It also involves the setting up of test pre-conditions. This kind of testing is most suitable for tests that are frequently carried out.
Now, I am having some problems with test harness. I read that it consists of a test suite of test cases, input files , output files, and test scripts. Now my question is what is the difference between test case and test script? Also, how do you use the software to test the different functions of the AUT? I also came across some terms like suite master and case agents.
Answer
Several broad questions there, will try to answer based on my experience.
Think of a Test Harness as an 'enabler' that actually does all the work of (1)executing tests using a (2)test library and (3)generating reports. It would require that your test scripts are designed to handle different (4)test data and (5)test scenarios. Essentially, when the test harness is in place and prerequisite data is prepared (aka data prep) someone should be able to click a button or run one command to execute all your tests and generate reports.
A test harness is most likely a collection of different things that make all of the above happen. If you wrote unit tests while developing your application, that would be part of a test harness. You would also have other tests for the functionality of your app, like: user logs in to site, sees favourites pane, recent messages and notifications. Then you add in a 'runner' of sorts that goes through all of your "test scripts" and runs them (instead of you having to execute tests one at a time). If it feels like a test harness is more of a conceptual collection rather than a single piece of software, then you're understanding this correctly :-)
Now my question is what is the difference between test case and test script?
Simple but not entirely correct answer: A Test Case defines test objectives, description, pre-conditions, steps (descriptive or specific), expected results. A Test Script would then be the actual automated script that you execute to do that test. That's in an Automation context. And it changes. A lot.
What certifications like ISTQB define as test scenarios is usually referred to as test cases in some companies and countries. In others, test cases are flipped with test scripts when referring to manual testing (when the steps are given in detail but not part of an automation harness). Others say that test scripts exclusively mean automated tests. On the other hand, one can also argue that several test cases can be combined in a test script and vice-versa. So that begs the question, how does a test procedure fit in?
A test development stage can have: "Test procedures, test scenarios, test cases, test datasets, test scripts to use in testing software."
If you assume a > (is larger than/collection of) relation, how would you relate those? Rhetorical question - that differs based on where you work, who your client is, etc. Best thing is to define it with your colleagues/clients and agree on the understanding of the terms rather than the definition. I currently go with test script = automated script, based on a pre-existing manual test case or a test scenario.
Also, how do you use the software to test the different functions of the AUT?
You write different tests to test different things. Each test does certain actions and checks if the AUT's output matches what you expected - If displayed_value == expected_value. An input file could be used to provide data for the test- list of test usernames and passwords, for instance. Or run the same test with different data - login as a different user with different messages, etc.
Take a look at RobotFramework and the Selenium. A robot framework test (written in text or html files) combined with the Selenium library would allow you to write an automated test which tests something specific...like a home page validation. You would write a separate test to ensure that a user can see all his/her messages. Another to test clearing notifications. And so on.