Hi Marcel,
here is an attempt at answering an old mail (this one was still in my client).
this breaks my preference... See below

Le jeu. 17 sept. 2020 à 15:41, <commits at source.squeak.org> a écrit :
>
> Marcel Taeumel uploaded a new version of MorphicTests to project The Trunk:
> http://source.squeak.org/trunk/MorphicTests-mt.65.mcz
>
> ==================== Summary ====================
>
> Name: MorphicTests-mt.65
> Author: mt
> Time: 17 September 2020, 3:41:47.157573 pm
> UUID: 50b2cc27-06d5-5d40-936d-7b029ddc01b1
> Ancestors: MorphicTests-mt.64, MorphicTests-ct.61
>
> Updates layout tests following MorphicTests-nice.61 (inbox->treated). Complements Morphic-mt.1683. Merges MorphicTests-ct.61 (inbox->trunk).
>
> =============== Diff against MorphicTests-mt.64 ===============
>
> Item was changed:
>   TestCase subclass: #MorphLayoutTest
> +       instanceVariableNames: 'reset'
> -       instanceVariableNames: ''
>         classVariableNames: ''
>         poolDictionaries: ''
>         category: 'MorphicTests-Layouts'!
>
> Item was removed:
> - ----- Method: MorphLayoutTest>>testScrollPaneBarUpdate (in category 'tests') -----
> - testScrollPaneBarUpdate
> -
> -       | oldPreferences |
> -       oldPreferences := ScrollPane useRetractableScrollBars.
> -       [| child container |
> -       ScrollPane useRetractableScrollBars: false.
> -       container := ScrollPane new color: Color green; extent: 300 @ 300; showVScrollBarOnlyWhenNeeded; showHScrollBarOnlyWhenNeeded.
> -       container scroller addMorphBack: (child := Morph new color: Color red; extent: 100 @ 100).
> -
> -       self ensureLayout: container.
> -       self assert: container hScrollBar owner isNil.
> -       self assert: container vScrollBar owner isNil.
> -
> -       child extent: 400 @ 100.
> -       self ensureLayout: container.
> -       self assert: container hScrollBar owner notNil.
> -       self assert: container vScrollBar owner isNil.
> -
> -       child extent: 400 @ 400.
> -       self ensureLayout: container.
> -       self assert: container hScrollBar owner notNil.
> -       self assert: container hScrollBar owner notNil]
> -               ensure: [ScrollPane useRetractableScrollBars: oldPreferences]!
>
> Item was added:
> + ----- Method: MorphicEventTests>>test02MouseOver (in category 'tests') -----
> + test02MouseOver
> +
> +       | m1 m2 |
> +       m1 := MorphForEventTests new.
> +       m2 := MorphForEventTests new.
> +
> +       m1 extent: 20 at 20; topLeft: 0 at 0.
> +       m2 extent: 20 at 20; topLeft: 40 at 0.
> +
> +       m1 openInWorld: world.
> +       m2 openInWorld: world.
> +
> +       hand handleEvent: (self redMouseDownAt: m1 center).
> +       hand handleEvent: (self redMouseUpAt: m1 center).
> +       hand handleEvent: (self redMouseDownAt: m2 center).
> +       hand handleEvent: (self redMouseUpAt: m2 center).
> +
> +       self
> +               checkEventOrder: #(mouseMove mouseEnter mouseDown mouseUp mouseLeave)
> +               forEvents: m1 eventsDuringBubble
> +               ignoreMouseOver: true.
> +
> +       self
> +               checkEventOrder: #(mouseMove mouseEnter mouseDown mouseUp)
> +               forEvents: m2 eventsDuringBubble
> +               ignoreMouseOver: true.
> +       !
>
> Item was removed:
> - ----- Method: MorphicEventTests>>test02MouserOver (in category 'tests') -----
> - test02MouserOver
> -
> -       | m1 m2 |
> -       m1 := MorphForEventTests new.
> -       m2 := MorphForEventTests new.
> -
> -       m1 extent: 20 at 20; topLeft: 0 at 0.
> -       m2 extent: 20 at 20; topLeft: 40 at 0.
> -
> -       m1 openInWorld: world.
> -       m2 openInWorld: world.
> -
> -       hand handleEvent: (self redMouseDownAt: m1 center).
> -       hand handleEvent: (self redMouseUpAt: m1 center).
> -       hand handleEvent: (self redMouseDownAt: m2 center).
> -       hand handleEvent: (self redMouseUpAt: m2 center).
> -
> -       self
> -               checkEventOrder: #(mouseMove mouseEnter mouseDown mouseUp mouseLeave)
> -               forEvents: m1 eventsDuringBubble
> -               ignoreMouseOver: true.
> -
> -       self
> -               checkEventOrder: #(mouseMove mouseEnter mouseDown mouseUp)
> -               forEvents: m2 eventsDuringBubble
> -               ignoreMouseOver: true.
> -       !
>
> Item was changed:
>   TestCase subclass: #TableLayoutTest
> +       instanceVariableNames: 'container reset'
> -       instanceVariableNames: 'container'
>         classVariableNames: ''
>         poolDictionaries: ''
>         category: 'MorphicTests-Layouts'!
>
> Item was added:
> + ----- Method: TableLayoutTest>>setUp (in category 'running') -----
> + setUp
> +
> +       super setUp.
> +
> +       reset := {
> +               ([:enable | [self useRetractableScrollBars: enable]]
> +                       value: self useRetractableScrollBars)
> +                       in: [:block | self useRetractableScrollBars: false].
> +       }.!

Hmph... This is brainfuck code... It should be:

    reset := {
        ([:enable | [self useRetractableScrollBars: enable]]
            value: self useRetractableScrollBars)
            in: [:block | self useRetractableScrollBars: false. block].
    }.

or just:

    reset := {
        ([:enable | [self useRetractableScrollBars: enable]]
            value: self useRetractableScrollBars)
    }.
    self useRetractableScrollBars: false

>
> Item was added:
> + ----- Method: TableLayoutTest>>tearDown (in category 'running') -----
> + tearDown
> +
> +       reset do: #value.
> +       super tearDown.!
>
> Item was changed:
>   ----- Method: TableLayoutTest>>testPluggableTextMorph (in category 'tests') -----
>   testPluggableTextMorph
>
> +       | ptm |
> -       | oldPreferences |
> -       oldPreferences := ScrollPane useRetractableScrollBars.
> -       [| ptm |
> -       ScrollPane useRetractableScrollBars: false.
>         ptm := PluggableTextMorph new
>                 extent: 100 at 50;
>                 setText: 'Hello World!! Hello World!! Hello World!! Hello World!!';
>                 wrapFlag: true.
> +
> -
>         container := self newContainer addMorphBack: ptm.
>         self ensureLayout: container.
>         self assert: 100 at 50 equals: container extent.
>
>         self assert: ptm vIsScrollbarShowing.
>         self deny: ptm hIsScrollbarShowing.
>
>         "Make it a one-liner."
>         ptm wrapFlag: false.
>         self ensureLayout: container.
>         self deny: ptm vIsScrollbarShowing.
>         self assert: ptm hIsScrollbarShowing.
>
>         "Make it a one-liner without the horizontal scrollbar."
>         ptm hideScrollBarsIndefinitely.
>         self ensureLayout: container.
>         self deny: ptm vIsScrollbarShowing.
> +       self deny: ptm hIsScrollbarShowing.
> -       self deny: ptm hIsScrollbarShowing]
> -               ensure: [ScrollPane useRetractableScrollBars: oldPreferences].
>   !
>
> Item was changed:
>   ----- Method: TableLayoutTest>>testPluggableTextMorphScrollBarNotNeeded (in category 'tests') -----
>   testPluggableTextMorphScrollBarNotNeeded
>         "The entire test might fit if the scroll bar would only disappear..."
>
> +       | ptm |
> -       | oldPreferences |
> -       oldPreferences := ScrollPane useRetractableScrollBars.
> -       [| ptm |
> -       ScrollPane useRetractableScrollBars: false.
>         ptm := PluggableTextMorph new
>                 extent: 100 at 50;
>                 setText: 'Hello World!! Hello World!! \\\ Hello World!! Hello World!!' withCRs.
>         container := self newContainer addMorphBack: ptm.
>
>         "Make it fit exactly first."
>         ptm hResizing: #shrinkWrap; vResizing: #shrinkWrap.
>         self ensureLayout: container.
>         ptm hResizing: #rigid; vResizing: #rigid.
>         ptm wrapFlag: true.
>
>         "No scrollbars required."
>         self ensureLayout: container.
>         self deny: ptm vIsScrollbarShowing.
>
>         "It wraps immediately."
>         ptm width: ptm width - 5.
>         self ensureLayout: container.
>         self assert: ptm vIsScrollbarShowing.
>
>         "No scrollbars required."
>         ptm width: ptm width + 5.
>         self ensureLayout: container.
> +       self deny: ptm vIsScrollbarShowing.!
> -       self deny: ptm vIsScrollbarShowing]
> -               ensure: [ScrollPane useRetractableScrollBars: oldPreferences]!
>
> Item was added:
> + ----- Method: TableLayoutTest>>testScrollPaneBarUpdate (in category 'tests - scroll panes') -----
> + testScrollPaneBarUpdate
> +
> +       | child container |
> +       container := ScrollPane new color: Color green; extent: 300 @ 300; showVScrollBarOnlyWhenNeeded; showHScrollBarOnlyWhenNeeded.
> +       container scroller addMorphBack: (child := Morph new color: Color red; extent: 100 @ 100).
> +
> +       self ensureLayout: container.
> +       self assert: container hScrollBar owner isNil.
> +       self assert: container vScrollBar owner isNil.
> +
> +       child extent: 400 @ 100.
> +       self ensureLayout: container.
> +       self assert: container hScrollBar owner notNil.
> +       self assert: container vScrollBar owner isNil.
> +
> +       child extent: 400 @ 400.
> +       self ensureLayout: container.
> +       self assert: container hScrollBar owner notNil.
> +       self assert: container hScrollBar owner notNil!
>
> Item was changed:
>   ----- Method: TableLayoutTest>>testScrollPaneShrinkWrap (in category 'tests') -----
>   testScrollPaneShrinkWrap
>
> +       | scroll scrollContent |
> -       | oldPreferences |
> -       oldPreferences := ScrollPane useRetractableScrollBars.
> -       [| scroll scrollContent |
> -       ScrollPane useRetractableScrollBars: false.
>         container := self newContainer
>                 vResizing: #rigid;
>                 addMorphBack: (self newMorph extent: 50 @ 50);
>                 addMorphBack: (scroll := ScrollPane new
>                         hResizing: #shrinkWrap;
>                         vResizing: #spaceFill;
>                         showVScrollBarOnlyWhenNeeded;
>                         hideHScrollBarIndefinitely).
>
>         " shrinkWrap the horizontal axis but scroll vertically "
>         scroll scroller
>                 layoutPolicy: TableLayout new;
>                 addMorphBack: (scrollContent := self newMorph extent: 200 @ 500).
>
>         container extent: 1 @ 300.
>         self ensureLayout: container.
>         self assert: container left = (container layoutChanged; fullBounds; left). "Do not be jumpy."
>         self assert: (200 + scroll scrollBarThickness + scroll borderWidth) @ 300 equals: scroll extent.
>
>         scrollContent extent: 300 @ 500.
>         self ensureLayout: container.
> +       self assert: (300 + scroll scrollBarThickness + scroll borderWidth) @ 300 equals: scroll extent!
> -       self assert: (300 + scroll scrollBarThickness + scroll borderWidth) @ 300 equals: scroll extent]
> -               ensure: [ScrollPane useRetractableScrollBars: oldPreferences].
> - !
>
> Item was added:
> + ----- Method: TableLayoutTest>>testScrollerFill (in category 'tests - scroll panes') -----
> + testScrollerFill
> +       "A scroll pane's scroller (i.e., the transform morph) has always #spaceFill behavior within the scroll pane's layout. Thus, submorphs (here: title and content) can themselves be #spaceFill. Embed a text morph to check height-for-width compatibility."
> +
> +       | content title |
> +       container := ScrollPane new.
> +
> +       container scroller
> +               layoutPolicy: TableLayout new;
> +               color: Color random;
> +               addMorphBack: (title := TextMorph new hResizing: #spaceFill; contents: 'Here comes an interesting title');
> +               addMorphBack: (content := self newMorph extent: 400 @ 400; hResizing: #spaceFill).
> +       container extent: 50 @ 50. "Pick an extent so that the title must wrap!!"
> +       self ensureLayout: container.
> +
> +       "container openInHand."
> +
> +       container extent: 500 @ 500.
> +       self ensureLayout: container.
> +       self assert: 500 @ 500 equals: container extent.
> +       self assert: 500 - (container borderWidth  * 2) @ 400 equals: content extent.
> +
> +       container extent: 300 @ 300.
> +       self ensureLayout: container.
> +       self assert: 300 @ 300 equals: container extent.
> +       self assert: 300 - container borderWidth - container scrollBarThickness @ 400 equals: content extent!
>
> Item was added:
> + ----- Method: TableLayoutTest>>testScrollerFillWithContainer (in category 'tests - scroll panes') -----
> + testScrollerFillWithContainer
> +       "A scroll pane's scroller (i.e., the transform morph) has always #spaceFill behavior within the scroll pane's layout. Thus, submorphs (here: title and content) can themselves be #spaceFill. Embed a text morph to check height-for-width compatibility. Add an extra container between scroller and title/content."
> +
> +       | content title |
> +       container := ScrollPane new.
> +
> +       container scroller
> +               layoutPolicy: TableLayout new;
> +               addMorphBack: (self newContainer
> +                       hResizing: #spaceFill;
> +                       vResizing: #spaceFill;
> +                       listDirection: #topToBottom;
> +                       addMorphBack: (title := TextMorph new hResizing: #spaceFill; contents: 'Here comes an interesting title');
> +                       addMorphBack: (content := self newMorph extent: 400 @ 400; hResizing: #spaceFill)).
> +       container extent: 50 @ 50. "Pick an extent so that the title must wrap!!"
> +       self ensureLayout: container.
> +
> +       "container openInHand."
> +
> +       container extent: 500 @ 500.
> +       self ensureLayout: container.
> +       self assert: 500 @ 500 equals: container extent.
> +       self assert: 500 - (container borderWidth  * 2) @ 400 equals: content extent.
> +
> +       container extent: 300 @ 300.
> +       self ensureLayout: container.
> +       self assert: 300 @ 300 equals: container extent.
> +       self assert: 300 - container borderWidth - container scrollBarThickness @ 400 equals: content extent!
>
> Item was changed:
>   ----- Method: TableLayoutTest>>testShrinkWrapScrollPaneAlwaysShowBars (in category 'tests') -----
>   testShrinkWrapScrollPaneAlwaysShowBars
>
> +       | scroll scrollContent |
> -       | oldPreferences |
> -       oldPreferences := ScrollPane useRetractableScrollBars.
> -       [| scroll scrollContent |
> -       ScrollPane useRetractableScrollBars: false.
>         container := self newContainer
>                 vResizing: #shrinkWrap;
>                 hResizing: #shrinkWrap;
>                 addMorphBack: (scroll := ScrollPane new
>                         hResizing: #shrinkWrap;
>                         vResizing: #shrinkWrap;
>                         alwaysShowHScrollBar;
>                         alwaysShowVScrollBar).
>
>         scroll scroller
>                 layoutPolicy: TableLayout new;
>                 addMorphBack: (scrollContent := self newMorph extent: 300 @ 300).
>
>         self ensureLayout: container.
> +       self assert: (300 @ 300) + scroll scrollBarThickness + scroll borderWidth equals: container extent!
> -       self assert: (300 @ 300) + scroll scrollBarThickness + scroll borderWidth equals: container extent]
> -               ensure: [ScrollPane useRetractableScrollBars: oldPreferences].
> - !
>
> Item was changed:
>   ----- Method: TableLayoutTest>>testSidebarAndScrollingView (in category 'tests - example layouts') -----
>   testSidebarAndScrollingView
>         " construct a container that has a fixed size sidebar on the left and a scrolling window that adapts flexibly to the container's size "
>
> +       | scrolling sidebar content title |
> -       | oldPreferences |
> -       oldPreferences := ScrollPane useRetractableScrollBars.
> -       [| scrolling sidebar content title |
> -       ScrollPane useRetractableScrollBars: false.
>         container := self newContainer
>                 addMorphBack: (sidebar := self newMorph width: 200; hResizing: #rigid; vResizing: #spaceFill);
>                 addMorphBack: (scrolling := ScrollPane new hResizing: #spaceFill; vResizing: #spaceFill).
>
>         scrolling scroller
>                 layoutPolicy: TableLayout new;
>                 addMorphBack: (self newContainer
>                         hResizing: #spaceFill;
>                         vResizing: #spaceFill;
>                         listDirection: #topToBottom;
>                         addMorphBack: (title := TextMorph new hResizing: #spaceFill; contents: 'Here comes a title');
>                         addMorphBack: (content := self newMorph extent: 400 @ 400; hResizing: #spaceFill)).
> +       self ensureLayout: container.
> +
>         "container openInHand."
>
>         container extent: 500 @ 500.
>         self ensureLayout: container.
>         self assert: 200 @ 500 equals: sidebar extent.
>         self assert: 300 @ 500 equals: scrolling extent.
>         self assert: 300 - (scrolling borderWidth  * 2) @ 400 equals: content extent.
>
>         container extent: 300 @ 300.
>         self ensureLayout: container.
>         self assert: 200 @ 300 equals: sidebar extent.
>         self assert: 100 @ 300 equals: scrolling extent.
> +       self assert: 100 - scrolling borderWidth - scrolling scrollBarThickness @ 400 equals: content extent!
> -       self assert: 100 - scrolling borderWidth - scrolling scrollBarThickness @ 400 equals: content extent]
> -               ensure: [ScrollPane useRetractableScrollBars: oldPreferences]!
>
> Item was added:
> + ----- Method: TableLayoutTest>>useRetractableScrollBars (in category 'running') -----
> + useRetractableScrollBars
> +
> +       ^ ScrollPane classPool at: #UseRetractableScrollBars!
>
> Item was added:
> + ----- Method: TableLayoutTest>>useRetractableScrollBars: (in category 'running') -----
> + useRetractableScrollBars: aBoolean
> +       "Re-implemented to avoid triggering #allSubInstancesDo:."
> +
> +       ScrollPane classPool at: #UseRetractableScrollBars put: aBoolean.!
>
>