scale: redo the test to avoid assuming resolution

Also drop "fractional", it's not only testing that.

mir-ci/mir_ci/tests/robot/suites/scale/scale.robot

@@ -0,0 +1,38 @@
+*** Settings ***
+Resource        ${KVM_RESOURCE}
+
+Suite Setup     Suite Setup
+Test Setup      Set Output Scale    ${SCALE}
+
+
+*** Variables ***
+${T}                        ${CURDIR}
+${SCREENSHOT}               ${T}/${SCALE}-gtk4-demo-screenshot.png
+${DEMO-APP-TITLE}           ${T}/${SCALE}-gtk4-demo-title-main.png
+${DEMO-APP-TITLE-HALF}      ${T}/${SCALE}-gtk4-demo-title-main-half.png
+${BUTTON}                   ${T}/${SCALE}-gtk4-demo-button.png
+${TITLE}                    ${T}/${SCALE}-gtk4-demo-title.png
+
+
+*** Test Cases ***
+Ensure Scaling Is Visually Correct
+    Move Pointer To Proportional (1.0, 1.0)
+
+    Match                   ${SCREENSHOT}
+
+Click Button With Scaling Enabled
+    Walk Pointer To ${BUTTON}
+    Click LEFT Button
+
+    Match                   ${TITLE}
+
+
+*** Keywords ***
+Suite Setup
+    Set Output Scale        ${SCALE}
+    # Work around https://github.com/canonical/mir/issues/3553
+    ${aligned}=             Run Keyword And Return Status
+    ...                     Walk Pointer To ${DEMO-APP-TITLE}
+    IF    ${aligned} == False    Walk Pointer To ${DEMO-APP-TITLE-HALF}
+    Click LEFT Button
+    Click LEFT Button

mir-ci/mir_ci/tests/test_fractional_scale_v1.py → mir-ci/mir_ci/tests/test_scale.py

@@ -51,7 +51,7 @@ def collect_assets(platform: str, resources: Collection[str], suite: str, varian
     },
 )
 @pytest.mark.env(GSETTINGS_BACKEND="keyfile")
-@pytest.mark.parametrize("server", servers(ServerCap.FLOATING_WINDOWS | ServerCap.DISPLAY_CONFIG))
+@pytest.mark.parametrize("server", servers(ServerCap.DISPLAY_CONFIG))
 @pytest.mark.parametrize("scale", [1.0, 1.5, 2.0])
 @pytest.mark.deps(
     debs=("gtk-4-examples",),
@@ -62,16 +62,17 @@ def collect_assets(platform: str, resources: Collection[str], suite: str, varian
         ("rpaframework-recognition", "RPA.recognition"),
     ),
 )
-class TestFractionalScaleV1:
-    async def test_fractional_scale_v1(self, robot_log, server, scale, tmp_path) -> None:
-        extensions = ("all",)  # TODO no need to enable all extensions
+class TestScale:
+    async def test_scale(self, robot_log, server, scale, tmp_path) -> None:
+        extensions = ("all",)  # TODO no need to enable all extension
+
         server_instance = DisplayServer(
             server,
             add_extensions=extensions,
             env={"MIR_SERVER_X11_OUTPUT": "1024x768", "MIR_SERVER_DISPLAY_SCALE": str(scale)},
         )
 
-        assets = collect_assets("wayland", ["kvm"], "fractional_scale_v1")
+        assets = collect_assets("wayland", ["kvm"], "scale")
 
         async with server_instance, server_instance.program(App(APP_PATH, AppType.deb)):
             tuple((tmp_path / k).symlink_to(v) for k, v in assets.items())