Fix test harness crashing on failure.

Author: xStrom

CHANGELOG.md

@@ -145,6 +145,7 @@ This means that druid no longer requires cairo on macOS and uses Core Graphics i
 - Added docs generation testing for all features. ([#942] by [@xStrom])
 - Renamed `BaseState` to `WidgetState` ([#969] by [@cmyr])
 - X11: Reworked error handling ([#982] by [@jneem])
+- Fixed test harness crashing on failure. ([#984] by [@xStrom])
 
 ### Outside News
 
@@ -231,6 +232,7 @@ This means that druid no longer requires cairo on macOS and uses Core Graphics i
 [#970]: https://github.com/xi-editor/druid/pull/970
 [#980]: https://github.com/xi-editor/druid/pull/980
 [#982]: https://github.com/xi-editor/druid/pull/982
+[#984]: https://github.com/xi-editor/druid/pull/984
 
 ## [0.5.0] - 2020-04-01
 

druid/src/tests/harness.rs

@@ -157,7 +157,6 @@ impl<T: Data> Harness<'_, T> {
                 window_size,
             };
             harness_closure(&mut harness);
-            harness.piet.finish().expect("piet finish failed");
         }
         render_context_closure(target)
     }
@@ -300,6 +299,16 @@ impl<T: Data> Inner<T> {
     }
 }
 
+impl<T> Drop for Harness<'_, T> {
+    fn drop(&mut self) {
+        // We need to call finish even if a test assert failed
+        if let Err(err) = self.piet.finish() {
+            // We can't panic, because we might already be panicking
+            log::error!("piet finish failed: {}", err);
+        }
+    }
+}
+
 impl Drop for TargetGuard<'_> {
     fn drop(&mut self) {
         // we need to call this to clean up the context