Test UI popup window with TestFX (ReplaceStringView.java)

[ningxie1991]

This pull requests relates to #6089, which is testing the UI using TestFX as suggested by @koppor. It also contributes to #6207 for adding more tests to the project. Test added:

ReplaceStringViewTest.java

This test uses TestFX to mock the ReplaceStringView and its fxml, brings up the dialogPane and executes a series of actions using FxRobot on the UI to verify the replace string action. However, it requires the Globals.prefs and Globals.fileUpdateMonitor variables to not be null, which implies a refactoring on the BaseDialog.java class and all its dependencies. Right now I initialized the Globals.prefs in the test to prove the concept that TestFX works.

Video of the test:
https://drive.google.com/file/d/1YTdLYF1SKNyjSvR9GRcz4Lv4S_yYzXcO/view?usp=sharing

Screenshot of the test:

• Change in CHANGELOG.md described in a way that is understandable for the average user (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked documentation: Is the information available and up to date? If not created an issue at https://github.com/JabRef/user-documentation/issues or, even better, submitted a pull request to the documentation repository.

[ningxie1991]

These are the lines of code that helped my test to run, because it needs Globals.prefs and Globals.fileUpdateMonitor to not be null.

[Siedlerchr]

Just an idea, can you try if Globals.prefs = mock(JabRefPreferences.class) works?
for Globals.fileUpdateMonitor you can try to use the DummyFileUpdateMonitor

[ningxie1991]

@Siedlerchr Yes it would work if we mock it up but I think the point is that we should not assign new value to Globals.prefs like this "Globals.prefs = ...." in the test. Because it's not like creating an instance of the object Globals and mock its prefs, for example, Globals globals = mock(Globals.class); globals.prefs = mock(JabRefPreferences.class);, but now we are directly setting the value of this global variable which is not ideal I think.

[Siedlerchr]

@JabRef/developers anyone an idea how to either extract the globals or how to test it?

[tobiasdiez]

In my opinion, it should suffices to test the view model. Then you don't need to worry about the whole gui setup, and it's more flexible. Using testfx should only be necessary in very rare instances (for example, to test complex actions that happen on focus or focus loss).

[koppor]

This PR showed that UI testing is really hard. - We should try to work on tests on components where code will be refactored (and the functionality should be kept) - or the functionality will be changed without breaking other desired functionality.

Since the JabRef team did not provice guidance for concrete components which sould be rewritten, finding an "awesome" component to write tests for is hard.

Maybe, the whole work on UI testing should be suspended and non-UI features should be worked on.