Support a tab structure

[BECATRUE]

This PR will close #196.

I supported a tab structure, not showing in a row.

[BECATRUE]

I will modify the unittest after implementing the central widget.

[BECATRUE]

Then, is there something to modify? @kangz12345

[kangz12345]

I will modify the unittest after implementing the central widget.

Is the unit test error expected?

[BECATRUE]

Is the unit test error expected?

No😮 I realized it just before and tried to fix it, but only unittest for Python 3.11 was failed.

[BECATRUE]

I found out the soluting using patch.object().

[kangz12345]

Why was it a problem only in 3.11? Do you know the exact cause?

[BECATRUE]

Why was it a problem only in 3.11? Do you know the exact cause?

Oh, I resolved it! I don't know the exact reason, but it looks like I did the wrong mocking.

[BECATRUE]

Please check this! @kangz12345 @Aijuh

[kangz12345]

I have 2 questions:

1. When we create an app at e.g. bottom and there were several frames (several columns), which one is tabified?
2. When we destroy an app whose frame was at e.g. bottom and there were 2 frames, will the remaining 1 frame be in a tab or not?

[BECATRUE]

When we create an app at e.g. bottom and there were several frames (several columns), which one is tabified?

In my simple test, a new frame is created in the frame with the latest added frame, because I used tabifyDockWidget() with the last element of areaDockWidgets as follows:

self.mainWindow.tabifyDockWidget(areaDockWidgets[-1], dockWidget)

If I use the first element areaDockWidgets[0], the frame is created in the frame with the first added frame as we expect.

[BECATRUE]

When we destroy an app whose frame was at e.g. bottom and there were 2 frames, will the remaining 1 frame be in a tab or not?

The remaining one is not in a tab, but just a single docked widget. It seems that PyQt doesn't support a tab with only a frame.

[kangz12345]

Thank you for the confirmation!

[BECATRUE]

Please re-check this PR! @Aijuh