[update-engine] fix buffer tests (#4163)

Apparently I'd made a couple of mistakes while writing tests:

* I was adding all events a second time by accident, which was hiding
  the fact that...
* A couple not signs were flipped, whoops.

update-engine/src/buffer.rs

@@ -1389,18 +1389,23 @@ mod tests {
         test_cx
             .run_filtered_test(
                 "all events passed in",
-                |buffer, event| buffer.add_event(event.clone()),
+                |buffer, event| {
+                    buffer.add_event(event.clone());
+                    true
+                },
                 WithDeltas::No,
             )
             .unwrap();
 
         test_cx
             .run_filtered_test(
                 "progress events skipped",
-                |buffer, event| {
-                    if let Event::Step(event) = event {
+                |buffer, event| match event {
+                    Event::Step(event) => {
                         buffer.add_step_event(event.clone());
+                        true
                     }
+                    Event::Progress(_) => false,
                 },
                 WithDeltas::Both,
             )
@@ -1410,13 +1415,16 @@ mod tests {
             .run_filtered_test(
                 "low-priority events skipped",
                 |buffer, event| match event {
-                    Event::Step(event) => {
-                        if event.kind.priority() == StepEventPriority::Low {
+                    Event::Step(event) => match event.kind.priority() {
+                        StepEventPriority::High => {
                             buffer.add_step_event(event.clone());
+                            true
                         }
-                    }
+                        StepEventPriority::Low => false,
+                    },
                     Event::Progress(event) => {
                         buffer.add_progress_event(event.clone());
+                        true
                     }
                 },
                 WithDeltas::Both,
@@ -1427,13 +1435,16 @@ mod tests {
             .run_filtered_test(
                 "low-priority and progress events skipped",
                 |buffer, event| match event {
-                    Event::Step(event) => {
-                        if event.kind.priority() == StepEventPriority::Low {
+                    Event::Step(event) => match event.kind.priority() {
+                        StepEventPriority::High => {
                             buffer.add_step_event(event.clone());
+                            true
                         }
-                    }
+                        StepEventPriority::Low => false,
+                    },
                     Event::Progress(_) => {
-                        // Don't add progress events either.
+                        // Don't add progress events.
+                        false
                     }
                 },
                 WithDeltas::Both,
@@ -1565,7 +1576,10 @@ mod tests {
         fn run_filtered_test(
             &self,
             event_fn_description: &str,
-            mut event_fn: impl FnMut(&mut EventBuffer<TestSpec>, &Event<TestSpec>),
+            mut event_fn: impl FnMut(
+                &mut EventBuffer<TestSpec>,
+                &Event<TestSpec>,
+            ) -> bool,
             with_deltas: WithDeltas,
         ) -> anyhow::Result<()> {
             match with_deltas {
@@ -1590,7 +1604,10 @@ mod tests {
 
         fn run_filtered_test_inner(
             &self,
-            mut event_fn: impl FnMut(&mut EventBuffer<TestSpec>, &Event<TestSpec>),
+            mut event_fn: impl FnMut(
+                &mut EventBuffer<TestSpec>,
+                &Event<TestSpec>,
+            ) -> bool,
             with_deltas: bool,
         ) -> anyhow::Result<()> {
             let description = format!("with deltas = {with_deltas}");
@@ -1608,8 +1625,9 @@ mod tests {
             let mut last_seen_opt = with_deltas.then_some(None);
 
             for (i, event) in self.generated_events.iter().enumerate() {
-                (event_fn)(&mut buffer, event);
-                buffer.add_event(event.clone());
+                // Going to use event_added in an upcoming commit.
+                let _event_added = (event_fn)(&mut buffer, event);
+
                 let report = match last_seen_opt {
                     Some(last_seen) => buffer.generate_report_since(last_seen),
                     None => buffer.generate_report(),