Add a testcase involving an expander

tests/a11y/expander.txt

@@ -0,0 +1,92 @@
+window1
+  "window"
+  index: 0
+  state: enabled resizable sensitive showing visible
+  toolkit: gail
+  <AtkComponent>
+  layer: window
+  alpha: 1
+  expander1
+    "toggle button"
+    parent: window1
+    index: 0
+    name: Reveal this
+    state: enabled expandable focusable sensitive showing visible
+    toolkit: gail
+    <AtkComponent>
+    layer: widget
+    alpha: 1
+    <AtkText>
+    text: Reveal this
+    character count: 11
+    caret offset: 0
+    default attributes: left-margin: 0
+                        right-margin: 0
+                        indent: 0
+                        invisible: false
+                        editable: false
+                        pixels-above-lines: 0
+                        pixels-below-lines: 0
+                        pixels-inside-wrap: 0
+                        bg-full-height: 0
+                        scale: 1
+                        rise: 0
+                        underline: none
+                        strikethrough: false
+                        bg-stipple: false
+                        fg-stipple: false
+                        fg-color: <omitted>
+                        bg-color: <omitted>
+                        wrap-mode: word
+                        justification: left
+                        size: <omitted>
+                        weight: <omitted>
+                        family-name: <omitted>
+                        stretch: <omitted>
+                        variant: <omitted>
+                        style: <omitted>
+                        language: <omitted>
+                        direction: <omitted>
+    <AtkAction>
+    action 0 name: activate
+    label1
+      "label"
+      parent: expander1
+      index: 0
+      name: Hello World!
+      state: enabled multi-line sensitive visible
+      toolkit: gail
+      <AtkComponent>
+      layer: widget
+      alpha: 1
+      <AtkText>
+      text: Hello World!
+      character count: 12
+      caret offset: 0
+      default attributes: left-margin: 0
+                          right-margin: 0
+                          indent: 0
+                          invisible: false
+                          editable: false
+                          pixels-above-lines: 0
+                          pixels-below-lines: 0
+                          pixels-inside-wrap: 0
+                          bg-full-height: 0
+                          scale: 1
+                          rise: 0
+                          underline: none
+                          strikethrough: false
+                          bg-stipple: false
+                          fg-stipple: false
+                          fg-color: <omitted>
+                          bg-color: <omitted>
+                          wrap-mode: word
+                          justification: left
+                          size: <omitted>
+                          weight: <omitted>
+                          family-name: <omitted>
+                          stretch: <omitted>
+                          variant: <omitted>
+                          style: <omitted>
+                          language: <omitted>
+                          direction: <omitted>