Fixes TipImageTests in org.eclipse.tips.tests #525

[Michael5601]

The content of the 4 disabled tests was very random before the change. There are 3 possibilities to deal with those tests:

1. Just delete the tests completely (which feels best for me)
2. Only test if setExtension has really set the extension by calling getExtension afterwards. (is very trivial and works only if the URL constructor was used because of the bad implementation of getExtension)
3. Use the solution presented in this PR (my problem with this solution is that it changes the too much of the old behavior and especially that the fields fURL and fBase64Image cannot be final anymore)

Can you please give me feedback to this?

[HeikoKlare]

@Michael5601 I'd propose you submit this proposal with suggested changes. Please write a commit message that is focussed on correcting setExtension of the TipImage rather than on fixing test, because that's what the PR will actually be about. Changes will require fBase64Image to not be final anymore, but fURL can remain final.

[HeikoKlare]

Since there is no specification saying that changing the extension shall actually change the URL but only the tag in the image string, I'd propose to simply change this as follows:

Suggested change

	if (isURLSet()) {
	String oldExtension = getExtension();
	try {
	fURL = new URL(fURL.toString().replace(oldExtension, newExtension));
	} catch (MalformedURLException e) {
	e.printStackTrace();
	}
	} else {
	int from = fBase64Image.indexOf('/') + 1;
	int to = fBase64Image.indexOf(';');
	String oldExtension = fBase64Image.substring(from, to).trim();
	fBase64Image = fBase64Image.replace(oldExtension, newExtension);
	}
	fBase64Image = fBase64Image.replaceAll("/.*;", "/" + extension + ";"); //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$
	}

Note that a replace operation based on the extension is not correct, as the substring with the extension can also appear at other places within the image string.

[HeikoKlare]

Testing the default.

Suggested change

	assertTrue(getTipImage().setExtension("png").getBase64Image().contains("png"));
	assertTrue(getTipImage().getBase64Image().contains("png"));

[HeikoKlare]

I would not expect the URL to change but only the Base64 contents. So tests should be equal to the ones in TipImageBase64Test with the only difference that the image is initialized via URL rather than via Base64 string.