it: add test for preferred buffer scale

src/it/test_config.rs

@@ -3,6 +3,7 @@ use {
         backend::InputDeviceId,
         ifs::wl_seat::SeatId,
         it::test_error::{TestError, TestResult},
+        tree::OutputNode,
         utils::{copyhashmap::CopyHashMap, stack::Stack},
     },
     bincode::Options,
@@ -15,6 +16,7 @@ use {
         },
         input::{InputDevice, Seat},
         keyboard::{Keymap, ModifiedKeySym},
+        video::Connector,
         Axis, Direction,
     },
     std::{cell::Cell, ops::Deref, ptr, rc::Rc},
@@ -251,6 +253,13 @@ impl TestConfig {
             }
         }
     }
+
+    pub fn set_scale(&self, output: &OutputNode, scale: f64) -> TestResult {
+        self.send(ClientMessage::ConnectorSetScale {
+            connector: Connector(output.global.connector.connector.id().raw() as _),
+            scale,
+        })
+    }
 }
 
 impl Drop for TestConfig {