Test style questions

[Robert Lichtenberger]

While discussing my Pull Request ([1]) for JDK-8176270 ([2]) with Jeanette
Winzenburg I came across two questions that I would like to ask the
community regarding test cases:

1) How fine-grained to we want tests to be? Is it ok to test two (somewhat
similiar) things at once or should a separate test case be written? e.g.
this test case of mine:
    @Test public void replaceSelectionAtEndWithListener() {
        StringBuilder selectedTextLog = new StringBuilder();
        StringBuilder selectionLog = new StringBuilder();
        textInput.setText("x xxx");
        textInput.selectRange(2, 5);
        textInput.selectedTextProperty().addListener((__, ___, selection)
-> selectedTextLog.append("|" + selection));
        textInput.selectionProperty().addListener((__, ___, selection) ->
selectionLog.append("|" + selection.getStart() + "," + selection.getEnd()));
        textInput.replaceSelection("a");
        assertEquals("|", selectedTextLog.toString());
        assertEquals("|3,3", selectionLog.toString());
        assertEquals("x a", textInput.getText());
    }
Will test the selectedTextProperty AND the selectionProperty at the same
time. Is this acceptable/desireable or should the test case be split into
two separate tests?

2) When fixing bugs, is it ok to not only provide a test case that will
fail before the fix and run successfully after the fix but also provide
additional test cases with the intention of preventing regressions? Ideally
of course such tests should already exist but what if they are not.
In my case I wanted to add a test case to "prove" that redo() will work in
the presence of a shortened text and I would also like to have a general
test case about selection properties and text property. What's the general
rule here?

Best regards,
Robert

[1] https://github.com/openjdk/jfx/pull/138
[2] https://bugs.openjdk.java.net/browse/JDK-8176270