Avoid real-rounding glitches near ends of a slider's range.

Floating point doesn't quite reliably satisfy certain standard
identities of arithmetic ...

Task-number: QTBUG-42358
Change-Id: I7417feedbfc1fd6f59510e0ee6d07d98ff7ddc46
Reviewed-by: Mitch Curtis <mitch.curtis@theqtcompany.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/tests/auto/controls/data/tst_slider.qml b/tests/auto/controls/data/tst_slider.qml
index 305605f6..1589f2ab 100644
--- a/tests/auto/controls/data/tst_slider.qml
+++ b/tests/auto/controls/data/tst_slider.qml
@@ -330,5 +330,32 @@ Item {
 
             control.destroy()
         }
+
+        function test_dragRounding() {
+            // Regression test: ends of range should be exact, not 99.99999999 &c.
+            var component = Qt.createComponent("slider/rounder.qml")
+            compare(component.status, Component.Ready)
+            var control = component.createObject(container)
+
+            // Does moving to maximum (100) actually reach it ?
+            mousePress(control, 0, control.waist)
+            mouseMove(control, control.width, control.waist)
+            mouseRelease(control, control.width, control.waist)
+            // Equality checks are dodgy with floats, but this should still be exact:
+            verify(control.value == 100)
+            // Neither of the following caught the bug, with value 100 -1.421e-14
+            // compare(control.value, 100)
+            // fuzzyCompare(control.value, 100, 1e-16)
+
+            // Now check it all works going the other way, too:
+            mousePress(control, control.width, control.waist)
+            mouseMove(control, 0, control.waist)
+            mouseRelease(control, 0, control.waist)
+            verify(control.value == 0)
+
+            // Tidy up.
+            control.destroy()
+            component.destroy()
+        }
     }
 }