diff --git a/packages/flutter_test/lib/src/frame_timing_summarizer.dart b/packages/flutter_test/lib/src/frame_timing_summarizer.dart
index 55bb67b97f..c6e3c464b8 100644
--- a/packages/flutter_test/lib/src/frame_timing_summarizer.dart
+++ b/packages/flutter_test/lib/src/frame_timing_summarizer.dart
@@ -294,16 +294,21 @@ class FrameTimingSummarizer {
       };
 }
 
-// The following helper functions require data sorted
-
-// return the 100*p-th percentile of the data
+/// Returns the 100*p-th percentile of [data].
+///
+/// [data] must be sorted in ascending order.
 T _findPercentile<T>(List<T> data, double p) {
   assert(p >= 0 && p <= 1);
   return data[((data.length - 1) * p).round()];
 }
 
-// return the number of items in data that > threshold
+/// Returns the number of elements in [data] that exceed [threshold].
+///
+/// [data] must be sorted in ascending order.
 int _countExceed<T extends Comparable<T>>(List<T> data, T threshold) {
-  return data.length -
-      data.indexWhere((T datum) => datum.compareTo(threshold) > 0);
+  final int exceedsThresholdIndex = data.indexWhere((T datum) => datum.compareTo(threshold) > 0);
+  if (exceedsThresholdIndex == -1) {
+    return 0;
+  }
+  return data.length - exceedsThresholdIndex;
 }
diff --git a/packages/flutter_test/test/frame_timing_summarizer_test.dart b/packages/flutter_test/test/frame_timing_summarizer_test.dart
index d58548a37f..0f11300936 100644
--- a/packages/flutter_test/test/frame_timing_summarizer_test.dart
+++ b/packages/flutter_test/test/frame_timing_summarizer_test.dart
@@ -7,51 +7,135 @@ import 'dart:ui';
 import 'package:flutter_test/flutter_test.dart';
 
 void main() {
-  test('Test FrameTimingSummarizer', () {
-    List<int> vsyncTimes = <int>[
-      for (int i = 0; i < 100; i += 1) 100 * (i + 1),
-    ];
-    List<int> buildTimes = <int>[
-      for (int i = 0; i < 100; i += 1) vsyncTimes[i] + 1000 * (i + 1),
-    ];
-    List<int> rasterTimes = <int>[
-      for (int i = 0; i < 100; i += 1) 1000 * (i + 1) + 1000,
-    ];
-    // reversed to make sure sort is working.
-    buildTimes = buildTimes.reversed.toList();
-    rasterTimes = rasterTimes.reversed.toList();
-    vsyncTimes = vsyncTimes.reversed.toList();
-    final List<FrameTiming> inputData = <FrameTiming>[
-      for (int i = 0; i < 100; i += 1)
-        FrameTiming(
-          vsyncStart: 0,
-          buildStart: vsyncTimes[i],
-          buildFinish: buildTimes[i],
-          rasterStart: 500,
-          rasterFinish: rasterTimes[i],
-          // Wall time should not be used in any profiling metrics.
-          // It is primarily to correlate with external tools' measurement.
-          rasterFinishWallTime: 0,
-        ),
-    ];
+  group(FrameTimingSummarizer, () {
+    test('calculates all fields', () {
+      List<int> vsyncTimes = <int>[
+        for (int i = 0; i < 100; i += 1) 100 * (i + 1),
+      ];
+      List<int> buildTimes = <int>[
+        for (int i = 0; i < 100; i += 1) vsyncTimes[i] + 1000 * (i + 1),
+      ];
+      List<int> rasterTimes = <int>[
+        for (int i = 0; i < 100; i += 1) 1000 * (i + 1) + 1000,
+      ];
+      // reversed to make sure sort is working.
+      buildTimes = buildTimes.reversed.toList();
+      rasterTimes = rasterTimes.reversed.toList();
+      vsyncTimes = vsyncTimes.reversed.toList();
+      final List<FrameTiming> inputData = <FrameTiming>[
+        for (int i = 0; i < 100; i += 1)
+          FrameTiming(
+            vsyncStart: 0,
+            buildStart: vsyncTimes[i],
+            buildFinish: buildTimes[i],
+            rasterStart: 500,
+            rasterFinish: rasterTimes[i],
+            // Wall time should not be used in any profiling metrics.
+            // It is primarily to correlate with external tools' measurement.
+            rasterFinishWallTime: 0,
+          ),
+      ];
 
-    final FrameTimingSummarizer summary = FrameTimingSummarizer(inputData);
-    expect(summary.averageFrameBuildTime.inMicroseconds, 50500);
-    expect(summary.p90FrameBuildTime.inMicroseconds, 90000);
-    expect(summary.p99FrameBuildTime.inMicroseconds, 99000);
-    expect(summary.worstFrameBuildTime.inMicroseconds, 100000);
-    expect(summary.missedFrameBuildBudget, 84);
+      final FrameTimingSummarizer summary = FrameTimingSummarizer(inputData);
+      expect(summary.averageFrameBuildTime.inMicroseconds, 50500);
+      expect(summary.p90FrameBuildTime.inMicroseconds, 90000);
+      expect(summary.p99FrameBuildTime.inMicroseconds, 99000);
+      expect(summary.worstFrameBuildTime.inMicroseconds, 100000);
+      expect(summary.missedFrameBuildBudget, 84);
 
-    expect(summary.averageFrameRasterizerTime.inMicroseconds, 51000);
-    expect(summary.p90FrameRasterizerTime.inMicroseconds, 90500);
-    expect(summary.p99FrameRasterizerTime.inMicroseconds, 99500);
-    expect(summary.worstFrameRasterizerTime.inMicroseconds, 100500);
-    expect(summary.missedFrameRasterizerBudget, 85);
-    expect(summary.frameBuildTime.length, 100);
+      expect(summary.averageFrameRasterizerTime.inMicroseconds, 51000);
+      expect(summary.p90FrameRasterizerTime.inMicroseconds, 90500);
+      expect(summary.p99FrameRasterizerTime.inMicroseconds, 99500);
+      expect(summary.worstFrameRasterizerTime.inMicroseconds, 100500);
+      expect(summary.missedFrameRasterizerBudget, 85);
+      expect(summary.frameBuildTime.length, 100);
 
-    expect(summary.averageVsyncOverhead.inMicroseconds, 5050);
-    expect(summary.p90VsyncOverhead.inMicroseconds, 9000);
-    expect(summary.p99VsyncOverhead.inMicroseconds, 9900);
-    expect(summary.worstVsyncOverhead.inMicroseconds, 10000);
+      expect(summary.averageVsyncOverhead.inMicroseconds, 5050);
+      expect(summary.p90VsyncOverhead.inMicroseconds, 9000);
+      expect(summary.p99VsyncOverhead.inMicroseconds, 9900);
+      expect(summary.worstVsyncOverhead.inMicroseconds, 10000);
+    });
+
+    group('missed budget count', () {
+      test('when single element missed budget', () {
+        final FrameTimingSummarizer summary = FrameTimingSummarizer(<FrameTiming>[
+          FrameTiming(
+            buildStart: 0,
+            buildFinish: (kBuildBudget + const Duration(microseconds: 1)).inMicroseconds,
+            vsyncStart: 0,
+            rasterStart: 0,
+            rasterFinish: 0,
+            rasterFinishWallTime: 0,
+          ),
+        ]);
+        expect(summary.missedFrameBuildBudget, 1);
+      });
+
+      test('when single element within budget', () {
+        final FrameTimingSummarizer summary = FrameTimingSummarizer(<FrameTiming>[
+          FrameTiming(
+            buildStart: 0,
+            buildFinish: 0,
+            vsyncStart: 0,
+            rasterStart: 0,
+            rasterFinish: 0,
+            rasterFinishWallTime: 0,
+          ),
+        ]);
+        expect(summary.missedFrameBuildBudget, 0);
+      });
+
+      test('when single element exactly within budget', () {
+        final FrameTimingSummarizer summary = FrameTimingSummarizer(<FrameTiming>[
+          FrameTiming(
+            buildStart: 0,
+            buildFinish: kBuildBudget.inMicroseconds,
+            vsyncStart: 0,
+            rasterStart: 0,
+            rasterFinish: 0,
+            rasterFinishWallTime: 0,
+          ),
+        ]);
+        expect(summary.missedFrameBuildBudget, 0);
+      });
+
+      test('when many missed budget', () {
+        final FrameTimingSummarizer summary = FrameTimingSummarizer(<FrameTiming>[
+          FrameTiming(
+            buildStart: 0,
+            buildFinish: 0,
+            vsyncStart: 0,
+            rasterStart: 0,
+            rasterFinish: 0,
+            rasterFinishWallTime: 0,
+          ),
+          FrameTiming(
+            buildStart: 0,
+            buildFinish: kBuildBudget.inMicroseconds,
+            vsyncStart: 0,
+            rasterStart: 0,
+            rasterFinish: 0,
+            rasterFinishWallTime: 0,
+          ),
+          FrameTiming(
+            buildStart: 0,
+            buildFinish: (kBuildBudget + const Duration(microseconds: 1)).inMicroseconds,
+            vsyncStart: 0,
+            rasterStart: 0,
+            rasterFinish: 0,
+            rasterFinishWallTime: 0,
+          ),
+          FrameTiming(
+            buildStart: 0,
+            buildFinish: (kBuildBudget + const Duration(microseconds: 2)).inMicroseconds,
+            vsyncStart: 0,
+            rasterStart: 0,
+            rasterFinish: 0,
+            rasterFinishWallTime: 0,
+          ),
+        ]);
+        expect(summary.missedFrameBuildBudget, 2);
+      });
+    });
   });
 }