diff --git a/dev/bots/analyze.dart b/dev/bots/analyze.dart
index 970225ca355..5f52765f6f7 100644
--- a/dev/bots/analyze.dart
+++ b/dev/bots/analyze.dart
@@ -2365,17 +2365,19 @@ Future<void> verifyNullInitializedDebugExpensiveFields(
     final _DebugOnlyFieldVisitor visitor = _DebugOnlyFieldVisitor(parsedFile);
     visitor.visitCompilationUnit(parsedFile.unit);
     for (final AstNode badNode in visitor.errors) {
-      errors.add('${file.path}:${parsedFile.lineInfo.getLocation(badNode.offset).lineNumber}');
+      errors.add(
+        '${file.path}:${parsedFile.lineInfo.getLocation(badNode.offset).lineNumber}: fields annotated with @_debugOnly must null initialize.',
+      );
     }
   }
   if (errors.isNotEmpty) {
     foundError(<String>[
-      '${bold}ERROR: ${red}fields annotated with @_debugOnly must null initialize.$reset',
-      'to ensure both the field and initializer are removed from profile/release mode.',
-      'These fields should be written as:\n',
-      'field = kDebugMode ? <DebugValue> : null;\n',
-      'Errors were found in the following files:',
       ...errors,
+      '',
+      '$bold${red}Fields annotated with @_debugOnly must null initialize,$reset',
+      'to ensure both the field and initializer are removed from profile/release mode.',
+      'These fields should be written as:',
+      'field = kDebugMode ? <DebugValue> : null;',
     ]);
   }
 }
@@ -2402,10 +2404,11 @@ Future<void> verifyTabooDocumentation(String workingDirectory, {int minimumMatch
   }
   if (errors.isNotEmpty) {
     foundError(<String>[
+      ...errors,
+      '',
       '${bold}Avoid the word "simply" in documentation. See https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#use-the-passive-voice-recommend-do-not-require-never-say-things-are-simple for details.$reset',
       '${bold}In many cases these words can be omitted without loss of generality; in other cases it may require a bit of rewording to avoid implying that the task is simple.$reset',
       '${bold}Similarly, avoid using "note:" or the phrase "note that". See https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#avoid-empty-prose for details.$reset',
-      ...errors,
     ]);
   }
 }
diff --git a/dev/bots/test/analyze-test-input/root/packages/flutter/lib/bar.dart b/dev/bots/test/analyze-test-input/root/packages/flutter/lib/bar.dart
index 578d559d310..97699608466 100644
--- a/dev/bots/test/analyze-test-input/root/packages/flutter/lib/bar.dart
+++ b/dev/bots/test/analyze-test-input/root/packages/flutter/lib/bar.dart
@@ -14,7 +14,7 @@ class Foo {
   final Map<String, String>? foo = kDebugMode ? <String, String>{} : null;
 
   @_debugOnly
-  final Map<String, String>? bar = kDebugMode ? null : <String, String>{};
+  final Map<String, String>? bar = kDebugMode ? null : <String, String>{}; // ERROR: fields annotated with @_debugOnly must null initialize.
 
   // dart format off
   // Checks the annotation works for multiline expressions.
@@ -24,36 +24,3 @@ class Foo {
     : null;
   // dart format on
 }
-
-/// Simply avoid this
-/// and simply do that.
-
-class ClassWithAClampMethod {
-  ClassWithAClampMethod clamp(double min, double max) => this;
-}
-
-void testNoDoubleClamp(int input) {
-  final ClassWithAClampMethod nonDoubleClamp = ClassWithAClampMethod();
-  // ignore: unnecessary_nullable_for_final_variable_declarations
-  final ClassWithAClampMethod? nonDoubleClamp2 = nonDoubleClamp;
-  // ignore: unnecessary_nullable_for_final_variable_declarations
-  final int? nullableInt = input;
-  final double? nullableDouble = nullableInt?.toDouble();
-
-  nonDoubleClamp.clamp(0, 2);
-  input.clamp(0, 2);
-  input.clamp(0.0, 2); // bad.
-  input.toDouble().clamp(0, 2); // bad.
-
-  nonDoubleClamp2?.clamp(0, 2);
-  nullableInt?.clamp(0, 2);
-  nullableInt?.clamp(0, 2.0); // bad
-  nullableDouble?.clamp(0, 2); // bad.
-
-  // ignore: unused_local_variable
-  final ClassWithAClampMethod Function(double, double)? tearOff1 = nonDoubleClamp2?.clamp;
-  // ignore: unused_local_variable
-  final num Function(num, num)? tearOff2 = nullableInt?.clamp; // bad.
-  // ignore: unused_local_variable
-  final num Function(num, num)? tearOff3 = nullableDouble?.clamp; // bad.
-}
diff --git a/dev/bots/test/analyze-test-input/root/packages/flutter/lib/double_clamp.dart b/dev/bots/test/analyze-test-input/root/packages/flutter/lib/double_clamp.dart
new file mode 100644
index 00000000000..10611299bea
--- /dev/null
+++ b/dev/bots/test/analyze-test-input/root/packages/flutter/lib/double_clamp.dart
@@ -0,0 +1,33 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+class ClassWithAClampMethod {
+  ClassWithAClampMethod clamp(double min, double max) => this;
+}
+
+void testNoDoubleClamp(int input) {
+  final ClassWithAClampMethod nonDoubleClamp = ClassWithAClampMethod();
+  // ignore: unnecessary_nullable_for_final_variable_declarations
+  final ClassWithAClampMethod? nonDoubleClamp2 = nonDoubleClamp;
+  // ignore: unnecessary_nullable_for_final_variable_declarations
+  final int? nullableInt = input;
+  final double? nullableDouble = nullableInt?.toDouble();
+
+  nonDoubleClamp.clamp(0, 2);
+  input.clamp(0, 2);
+  input.clamp(0.0, 2); // ERROR: input.clamp(0.0, 2)
+  input.toDouble().clamp(0, 2); // ERROR: input.toDouble().clamp(0, 2)
+
+  nonDoubleClamp2?.clamp(0, 2);
+  nullableInt?.clamp(0, 2);
+  nullableInt?.clamp(0, 2.0); // ERROR: nullableInt?.clamp(0, 2.0)
+  nullableDouble?.clamp(0, 2); // ERROR: nullableDouble?.clamp(0, 2)
+
+  // ignore: unused_local_variable
+  final ClassWithAClampMethod Function(double, double)? tearOff1 = nonDoubleClamp2?.clamp;
+  // ignore: unused_local_variable
+  final num Function(num, num)? tearOff2 = nullableInt?.clamp; // ERROR: nullableInt?.clamp
+  // ignore: unused_local_variable
+  final num Function(num, num)? tearOff3 = nullableDouble?.clamp; // ERROR: nullableDouble?.clamp
+}
diff --git a/dev/bots/test/analyze-test-input/root/packages/flutter/lib/renderbox_intrinsics.dart b/dev/bots/test/analyze-test-input/root/packages/flutter/lib/renderbox_intrinsics.dart
index 412863a85ee..4342be20da6 100644
--- a/dev/bots/test/analyze-test-input/root/packages/flutter/lib/renderbox_intrinsics.dart
+++ b/dev/bots/test/analyze-test-input/root/packages/flutter/lib/renderbox_intrinsics.dart
@@ -9,31 +9,32 @@ mixin ARenderBoxMixin on RenderBox {
   void computeMaxIntrinsicWidth() {}
 
   @override
-  void computeMinIntrinsicWidth() => computeMaxIntrinsicWidth(); // BAD
+  void computeMinIntrinsicWidth() => computeMaxIntrinsicWidth(); // ERROR: computeMaxIntrinsicWidth(). Consider calling getMaxIntrinsicWidth instead.
 
   @override
   void computeMinIntrinsicHeight() {
-    final void Function() f = computeMaxIntrinsicWidth; // BAD
+    final void Function() f =
+        computeMaxIntrinsicWidth; // ERROR: f = computeMaxIntrinsicWidth. Consider calling getMaxIntrinsicWidth instead.
     f();
   }
 }
 
 extension ARenderBoxExtension on RenderBox {
   void test() {
-    computeDryBaseline(); // BAD
-    computeDryLayout(); // BAD
+    computeDryBaseline(); // ERROR: computeDryBaseline(). Consider calling getDryBaseline instead.
+    computeDryLayout(); // ERROR: computeDryLayout(). Consider calling getDryLayout instead.
   }
 }
 
 class RenderBoxSubclass1 extends RenderBox {
   @override
   void computeDryLayout() {
-    computeDistanceToActualBaseline(); // BAD
+    computeDistanceToActualBaseline(); // ERROR: computeDistanceToActualBaseline(). Consider calling getDistanceToBaseline, or getDistanceToActualBaseline instead.
   }
 
   @override
   void computeDistanceToActualBaseline() {
-    computeMaxIntrinsicHeight(); // BAD
+    computeMaxIntrinsicHeight(); // ERROR: computeMaxIntrinsicHeight(). Consider calling getMaxIntrinsicHeight instead.
   }
 }
 
diff --git a/dev/bots/test/analyze-test-input/root/packages/flutter/lib/stopwatch.dart b/dev/bots/test/analyze-test-input/root/packages/flutter/lib/stopwatch.dart
index 722ace367a0..1a919173271 100644
--- a/dev/bots/test/analyze-test-input/root/packages/flutter/lib/stopwatch.dart
+++ b/dev/bots/test/analyze-test-input/root/packages/flutter/lib/stopwatch.dart
@@ -17,48 +17,48 @@ void testNoStopwatches(Stopwatch stopwatch) {
   // OK for now, but we probably want to catch public APIs that take a Stopwatch?
   stopwatch.runtimeType;
   // Bad: introducing Stopwatch from dart:core.
-  final Stopwatch localVariable = Stopwatch();
+  final Stopwatch localVariable = Stopwatch(); // ERROR: Stopwatch()
   // Bad: introducing Stopwatch from dart:core.
-  Stopwatch().runtimeType;
+  Stopwatch().runtimeType; // ERROR: Stopwatch()
 
   (localVariable..runtimeType) // OK: not directly introducing Stopwatch.
       .runtimeType;
 
   // Bad: introducing a Stopwatch subclass.
-  StopwatchAtHome().runtimeType;
+  StopwatchAtHome().runtimeType; // ERROR: StopwatchAtHome()
 
   // OK: not directly introducing Stopwatch.
   Stopwatch anotherStopwatch = stopwatch;
   // Bad: introducing a Stopwatch constructor.
-  StopwatchAtHome Function() constructor = StopwatchAtHome.new;
+  StopwatchAtHome Function() constructor = StopwatchAtHome.new; // ERROR: StopwatchAtHome.new
   assert(() {
     anotherStopwatch = constructor()..runtimeType;
     // Bad: introducing a Stopwatch constructor.
-    constructor = StopwatchAtHome.create;
+    constructor = StopwatchAtHome.create; // ERROR: StopwatchAtHome.create
     anotherStopwatch = constructor()..runtimeType;
     return true;
   }());
   anotherStopwatch.runtimeType;
 
   // Bad: introducing an external Stopwatch constructor.
-  externallib.MyStopwatch.create();
+  externallib.MyStopwatch.create(); // ERROR: externallib.MyStopwatch.create()
   ExternalStopwatchConstructor? externalConstructor;
 
   assert(() {
     // Bad: introducing an external Stopwatch constructor.
-    externalConstructor = externallib.MyStopwatch.new;
+    externalConstructor = externallib.MyStopwatch.new; // ERROR: externallib.MyStopwatch.new
     return true;
   }());
   externalConstructor?.call();
 
   // Bad: introducing an external Stopwatch.
-  externallib.stopwatch.runtimeType;
+  externallib.stopwatch.runtimeType; // ERROR: externallib.stopwatch
   // Bad: calling an external function that returns a Stopwatch.
-  externallib.createMyStopwatch().runtimeType;
+  externallib.createMyStopwatch().runtimeType; // ERROR: externallib.createMyStopwatch()
   // Bad: calling an external function that returns a Stopwatch.
-  externallib.createStopwatch().runtimeType;
+  externallib.createStopwatch().runtimeType; // ERROR: externallib.createStopwatch()
   // Bad: introducing the tear-off form of an external function that returns a Stopwatch.
-  externalConstructor = externallib.createMyStopwatch;
+  externalConstructor = externallib.createMyStopwatch; // ERROR: externallib.createMyStopwatch
 
   // OK: existing instance.
   constructor.call().stopwatch;
diff --git a/dev/bots/test/analyze-test-input/root/packages/flutter/lib/taboo_words.dart b/dev/bots/test/analyze-test-input/root/packages/flutter/lib/taboo_words.dart
new file mode 100644
index 00000000000..99a3dfff6e0
--- /dev/null
+++ b/dev/bots/test/analyze-test-input/root/packages/flutter/lib/taboo_words.dart
@@ -0,0 +1,7 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+/// Simply avoid this // ERROR: Found use of the taboo word "Simply" in documentation string.
+/// and simply do that. // ERROR: Found use of the taboo word "Simply" in documentation string.
+T id<T>(T x) => x;
diff --git a/dev/bots/test/analyze-test-input/root/packages/foo/deprecation.dart b/dev/bots/test/analyze-test-input/root/packages/foo/deprecation.dart
index 022fde5559c..02cb9f9cb65 100644
--- a/dev/bots/test/analyze-test-input/root/packages/foo/deprecation.dart
+++ b/dev/bots/test/analyze-test-input/root/packages/foo/deprecation.dart
@@ -11,26 +11,26 @@ void test1() {}
 // The code below is intentionally miss-formatted for testing.
 // dart format off
 @Deprecated(
-  'bad grammar. '
+  'bad grammar. '  // ERROR: Deprecation notice should be a grammatically correct sentence and start with a capital letter; see style guide: https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md
   'This feature was deprecated after v1.2.3.'
 )
 void test2() { }
 
 @Deprecated(
-  'Also bad grammar '
+  'Also bad grammar ' // ERROR: Deprecation notice should be a grammatically correct sentence and end with a period; notice appears to be "Also bad grammar".
   'This feature was deprecated after v1.2.3.'
 )
 void test3() { }
 
-@Deprecated('Not the right syntax. This feature was deprecated after v1.2.3.')
+@Deprecated('Not the right syntax. This feature was deprecated after v1.2.3.') // ERROR: Deprecation notice must be an adjacent string.
 void test4() { }
 
-@Deprecated(
+@Deprecated( // ERROR: Deprecation notice must be an adjacent string.
   'Missing the version line. '
 )
 void test5() { }
 
-@Deprecated(
+@Deprecated( // ERROR: Deprecation notice must be an adjacent string.
   'This feature was deprecated after v1.2.3.'
 )
 void test6() { }
@@ -49,13 +49,13 @@ void test8() { }
 
 @Deprecated(
   'Version number test (should fail). '
-  'This feature was deprecated after v1.20.0.'
+  'This feature was deprecated after v1.20.0.' // ERROR: Deprecation notice does not accurately indicate a beta branch version number; please see https://flutter.dev/docs/development/tools/sdk/releases to find the latest beta build version number.
 )
 void test9() { }
 
 @Deprecated(
   'Version number test (should fail). '
-  'This feature was deprecated after v1.21.0.'
+  'This feature was deprecated after v1.21.0.' // ERROR: Deprecation notice does not accurately indicate a beta branch version number; please see https://flutter.dev/docs/development/tools/sdk/releases to find the latest beta build version number.
 )
 void test10() { }
 
@@ -78,7 +78,7 @@ void test12() { }
 void test13() { }
 
 @Deprecated(
-  "Double quotes' test (should fail). "
+  "Double quotes' test (should fail). " // ERROR: Deprecation notice does not match required pattern. You might have used double quotes (") for the string instead of single quotes (').
   'This feature was deprecated after v2.1.0-11.0.pre.'
 )
 void test14() { }
diff --git a/dev/bots/test/analyze-test-input/root/packages/foo/meta.dart b/dev/bots/test/analyze-test-input/root/packages/foo/meta.dart
new file mode 100644
index 00000000000..b1e97489166
--- /dev/null
+++ b/dev/bots/test/analyze-test-input/root/packages/foo/meta.dart
@@ -0,0 +1,6 @@
+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// ERROR: error #1 // ERROR: error #2
+// ERROR: error #3
diff --git a/dev/bots/test/analyze_test.dart b/dev/bots/test/analyze_test.dart
index d5510f9c83f..5ea0559003c 100644
--- a/dev/bots/test/analyze_test.dart
+++ b/dev/bots/test/analyze_test.dart
@@ -54,40 +54,34 @@ void main() {
   );
   final String testGenDefaultsPath = path.join('test', 'analyze-gen-defaults');
 
+  test('matchesErrorsInFile matcher basic test', () async {
+    final String result = await capture(() async {
+      foundError(<String>[
+        'meta.dart:5: error #1',
+        'meta.dart:5: error #2',
+        'meta.dart:6: error #3',
+        '',
+        'Error summary',
+      ]);
+    }, shouldHaveErrors: true);
+    final File fixture = File(path.join(testRootPath, 'packages', 'foo', 'meta.dart'));
+    expect(result, matchesErrorsInFile(fixture, endsWith: <String>['', 'Error summary']));
+  });
+
   test('analyze.dart - verifyDeprecations', () async {
     final String result = await capture(
       () => verifyDeprecations(testRootPath, minimumMatches: 2),
       shouldHaveErrors: true,
     );
-    final String lines = <String>[
-          '║ test/analyze-test-input/root/packages/foo/deprecation.dart:14: Deprecation notice should be a grammatically correct sentence and start with a capital letter; see style guide: STYLE_GUIDE_URL',
-          '║ test/analyze-test-input/root/packages/foo/deprecation.dart:20: Deprecation notice should be a grammatically correct sentence and end with a period; notice appears to be "Also bad grammar".',
-          '║ test/analyze-test-input/root/packages/foo/deprecation.dart:25: Deprecation notice must be an adjacent string.',
-          '║ test/analyze-test-input/root/packages/foo/deprecation.dart:28: Deprecation notice must be an adjacent string.',
-          '║ test/analyze-test-input/root/packages/foo/deprecation.dart:33: Deprecation notice must be an adjacent string.',
-          '║ test/analyze-test-input/root/packages/foo/deprecation.dart:52: Deprecation notice does not accurately indicate a beta branch version number; please see RELEASES_URL to find the latest beta build version number.',
-          '║ test/analyze-test-input/root/packages/foo/deprecation.dart:58: Deprecation notice does not accurately indicate a beta branch version number; please see RELEASES_URL to find the latest beta build version number.',
-          '║ test/analyze-test-input/root/packages/foo/deprecation.dart:81: Deprecation notice does not match required pattern. You might have used double quotes (") for the string instead of single quotes (\').',
-        ]
-        .map((String line) {
-          return line
-              .replaceAll('/', Platform.isWindows ? r'\' : '/')
-              .replaceAll(
-                'STYLE_GUIDE_URL',
-                'https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md',
-              )
-              .replaceAll(
-                'RELEASES_URL',
-                'https://flutter.dev/docs/development/tools/sdk/releases',
-              );
-        })
-        .join('\n');
+    final File fixture = File(path.join(testRootPath, 'packages', 'foo', 'deprecation.dart'));
     expect(
       result,
-      '╔═╡ERROR #1╞════════════════════════════════════════════════════════════════════\n'
-      '$lines\n'
-      '║ See: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes\n'
-      '╚═══════════════════════════════════════════════════════════════════════════════\n',
+      matchesErrorsInFile(
+        fixture,
+        endsWith: <String>[
+          'See: https://github.com/flutter/flutter/blob/main/docs/contributing/Tree-hygiene.md#handling-breaking-changes',
+        ],
+      ),
     );
   });
 
@@ -279,15 +273,20 @@ void main() {
       shouldHaveErrors: true,
     );
 
-    expect(result, isNot(contains(':13')));
-    expect(result, isNot(contains(':14')));
-    expect(result, isNot(contains(':15')));
-    expect(result, isNot(contains(':19')));
-    expect(result, isNot(contains(':20')));
-    expect(result, isNot(contains(':21')));
-    expect(result, isNot(contains(':22')));
-
-    expect(result, contains(':17'));
+    final File fixture = File(path.join(testRootPath, 'packages', 'flutter', 'lib', 'bar.dart'));
+    expect(
+      result,
+      matchesErrorsInFile(
+        fixture,
+        endsWith: <String>[
+          '',
+          'Fields annotated with @_debugOnly must null initialize,',
+          'to ensure both the field and initializer are removed from profile/release mode.',
+          'These fields should be written as:',
+          'field = kDebugMode ? <DebugValue> : null;',
+        ],
+      ),
+    );
   });
 
   test('analyze.dart - verifyTabooDocumentation', () async {
@@ -296,9 +295,21 @@ void main() {
       shouldHaveErrors: true,
     );
 
-    expect(result, isNot(contains(':27')));
-    expect(result, contains(':28'));
-    expect(result, contains(':29'));
+    final File fixture = File(
+      path.join(testRootPath, 'packages', 'flutter', 'lib', 'taboo_words.dart'),
+    );
+    expect(
+      result,
+      matchesErrorsInFile(
+        fixture,
+        endsWith: <String>[
+          '',
+          'Avoid the word "simply" in documentation. See https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#use-the-passive-voice-recommend-do-not-require-never-say-things-are-simple for details.',
+          'In many cases these words can be omitted without loss of generality; in other cases it may require a bit of rewording to avoid implying that the task is simple.',
+          'Similarly, avoid using "note:" or the phrase "note that". See https://github.com/flutter/flutter/blob/main/docs/contributing/Style-guide-for-Flutter-repo.md#avoid-empty-prose for details.',
+        ],
+      ),
+    );
   });
 
   test('analyze.dart - clampDouble', () async {
@@ -310,21 +321,19 @@ void main() {
       ),
       shouldHaveErrors: true,
     );
-    final String lines = <String>[
-      '║ packages/flutter/lib/bar.dart:45: input.clamp(0.0, 2)',
-      '║ packages/flutter/lib/bar.dart:46: input.toDouble().clamp(0, 2)',
-      '║ packages/flutter/lib/bar.dart:50: nullableInt?.clamp(0, 2.0)',
-      '║ packages/flutter/lib/bar.dart:51: nullableDouble?.clamp(0, 2)',
-      '║ packages/flutter/lib/bar.dart:56: nullableInt?.clamp',
-      '║ packages/flutter/lib/bar.dart:58: nullableDouble?.clamp',
-    ].map((String line) => line.replaceAll('/', Platform.isWindows ? r'\' : '/')).join('\n');
+
+    final File fixture = File(
+      path.join(testRootPath, 'packages', 'flutter', 'lib', 'double_clamp.dart'),
+    );
     expect(
       result,
-      '╔═╡ERROR #1╞════════════════════════════════════════════════════════════════════\n'
-      '$lines\n'
-      '║ \n'
-      '║ For performance reasons, we use a custom "clampDouble" function instead of using "double.clamp".\n'
-      '╚═══════════════════════════════════════════════════════════════════════════════\n',
+      matchesErrorsInFile(
+        fixture,
+        endsWith: <String>[
+          '', // empty line before the last sentence.
+          'For performance reasons, we use a custom "clampDouble" function instead of using "double.clamp".',
+        ],
+      ),
     );
   });
 
@@ -337,27 +346,20 @@ void main() {
       ),
       shouldHaveErrors: true,
     );
-    final String lines = <String>[
-      '║ packages/flutter/lib/stopwatch.dart:20: Stopwatch()',
-      '║ packages/flutter/lib/stopwatch.dart:22: Stopwatch()',
-      '║ packages/flutter/lib/stopwatch.dart:28: StopwatchAtHome()',
-      '║ packages/flutter/lib/stopwatch.dart:33: StopwatchAtHome.new',
-      '║ packages/flutter/lib/stopwatch.dart:37: StopwatchAtHome.create',
-      '║ packages/flutter/lib/stopwatch.dart:44: externallib.MyStopwatch.create()',
-      '║ packages/flutter/lib/stopwatch.dart:49: externallib.MyStopwatch.new',
-      '║ packages/flutter/lib/stopwatch.dart:55: externallib.stopwatch',
-      '║ packages/flutter/lib/stopwatch.dart:57: externallib.createMyStopwatch()',
-      '║ packages/flutter/lib/stopwatch.dart:59: externallib.createStopwatch()',
-      '║ packages/flutter/lib/stopwatch.dart:61: externallib.createMyStopwatch',
-    ].map((String line) => line.replaceAll('/', Platform.isWindows ? r'\' : '/')).join('\n');
+
+    final File fixture = File(
+      path.join(testRootPath, 'packages', 'flutter', 'lib', 'stopwatch.dart'),
+    );
     expect(
       result,
-      '╔═╡ERROR #1╞════════════════════════════════════════════════════════════════════\n'
-      '$lines\n'
-      '║ \n'
-      '║ Stopwatches introduce flakes by falling out of sync with the FakeAsync used in testing.\n'
-      '║ A Stopwatch that stays in sync with FakeAsync is available through the Gesture or Test bindings, through samplingClock.\n'
-      '╚═══════════════════════════════════════════════════════════════════════════════\n',
+      matchesErrorsInFile(
+        fixture,
+        endsWith: <String>[
+          '',
+          'Stopwatches introduce flakes by falling out of sync with the FakeAsync used in testing.',
+          'A Stopwatch that stays in sync with FakeAsync is available through the Gesture or Test bindings, through samplingClock.',
+        ],
+      ),
     );
   });
 
@@ -370,21 +372,18 @@ void main() {
       ),
       shouldHaveErrors: true,
     );
-    final String lines = <String>[
-      '║ packages/flutter/lib/renderbox_intrinsics.dart:12: computeMaxIntrinsicWidth(). Consider calling getMaxIntrinsicWidth instead.',
-      '║ packages/flutter/lib/renderbox_intrinsics.dart:16: f = computeMaxIntrinsicWidth. Consider calling getMaxIntrinsicWidth instead.',
-      '║ packages/flutter/lib/renderbox_intrinsics.dart:23: computeDryBaseline(). Consider calling getDryBaseline instead.',
-      '║ packages/flutter/lib/renderbox_intrinsics.dart:24: computeDryLayout(). Consider calling getDryLayout instead.',
-      '║ packages/flutter/lib/renderbox_intrinsics.dart:31: computeDistanceToActualBaseline(). Consider calling getDistanceToBaseline, or getDistanceToActualBaseline instead.',
-      '║ packages/flutter/lib/renderbox_intrinsics.dart:36: computeMaxIntrinsicHeight(). Consider calling getMaxIntrinsicHeight instead.',
-    ].map((String line) => line.replaceAll('/', Platform.isWindows ? r'\' : '/')).join('\n');
+    final File fixture = File(
+      path.join(testRootPath, 'packages', 'flutter', 'lib', 'renderbox_intrinsics.dart'),
+    );
     expect(
       result,
-      '╔═╡ERROR #1╞════════════════════════════════════════════════════════════════════\n'
-      '$lines\n'
-      '║ \n'
-      '║ Typically the get* methods should be used to obtain the intrinsics of a RenderBox.\n'
-      '╚═══════════════════════════════════════════════════════════════════════════════\n',
+      matchesErrorsInFile(
+        fixture,
+        endsWith: <String>[
+          '',
+          'Typically the get* methods should be used to obtain the intrinsics of a RenderBox.',
+        ],
+      ),
     );
   });
 
diff --git a/dev/bots/test/common.dart b/dev/bots/test/common.dart
index 0a697ad8223..67088acfcf2 100644
--- a/dev/bots/test/common.dart
+++ b/dev/bots/test/common.dart
@@ -3,9 +3,13 @@
 // found in the LICENSE file.
 
 import 'dart:io';
+import 'dart:math' as math;
 
+import 'package:collection/collection.dart';
 import 'package:test/test.dart';
 
+import '../utils.dart';
+
 export 'package:test/test.dart' hide isInstanceOf;
 
 /// A matcher that compares the type of the actual value to the type argument T.
@@ -31,3 +35,188 @@ Matcher throwsExceptionWith(String messageSubString) {
     ),
   );
 }
+
+/// A matcher that matches error messages specified in the given `fixture` [File].
+///
+/// This matcher allows analyzer tests to specify the expected error messages
+/// in the test fixture file, eliminating the need to hard code line numbers in
+/// the test.
+///
+/// The error messages must be printed using the [foundError] function. Each
+/// error must start with the path to the file where the error resides, line
+/// number (1-based instead of 0-based) of the error, and a short description,
+/// delimited by colons (`:`). In the test fixture one could add the following
+/// comment on the line that would produce the error, to tell matcher what to
+/// expect:
+/// `// ERROR: <error message without the leading path and line number>`.
+Matcher matchesErrorsInFile(File fixture, {List<String> endsWith = const <Never>[]}) =>
+    _ErrorMatcher(fixture, endsWith);
+
+class _ErrorMatcher extends Matcher {
+  _ErrorMatcher(this.file, this.endsWith) : bodyMatcher = _ErrorsInFileMatcher(file);
+
+  static const String mismatchDescriptionKey = 'mismatchDescription';
+  static final int _errorBoxWidth = math.max(15, (hasColor ? stdout.terminalColumns : 80) - 1);
+  static const String _title = 'ERROR #1';
+  static final String _firstLine = '╔═╡$_title╞═${"═" * (_errorBoxWidth - 4 - _title.length)}';
+
+  static final String _lastLine = '╚${"═" * _errorBoxWidth}';
+  static const String _linePrefix = '║ ';
+
+  static bool mismatch(String mismatchDescription, Map<dynamic, dynamic> matchState) {
+    matchState[mismatchDescriptionKey] = mismatchDescription;
+    return false;
+  }
+
+  final List<String> endsWith;
+  final File file;
+  final _ErrorsInFileMatcher bodyMatcher;
+
+  @override
+  bool matches(dynamic item, Map<dynamic, dynamic> matchState) {
+    if (item is! String) {
+      return mismatch('expected a String, got $item', matchState);
+    }
+    final List<String> lines = item.split('\n');
+    if (lines.isEmpty) {
+      return mismatch('the actual error message is empty', matchState);
+    }
+    if (lines.first != _firstLine) {
+      return mismatch(
+        'the first line of the error message must be $_firstLine, got ${lines.first}',
+        matchState,
+      );
+    }
+    if (lines.last.isNotEmpty) {
+      return mismatch(
+        'missing newline at the end of the error message, got ${lines.last}',
+        matchState,
+      );
+    }
+    if (lines[lines.length - 2] != _lastLine) {
+      return mismatch(
+        'the last line of the error message must be $_lastLine, got ${lines[lines.length - 2]}',
+        matchState,
+      );
+    }
+    final List<String> body = lines.sublist(1, lines.length - 2);
+    final String? noprefix = body.firstWhereOrNull((String line) => !line.startsWith(_linePrefix));
+    if (noprefix != null) {
+      return mismatch(
+        'Line "$noprefix" should start with a prefix $_linePrefix..\n$lines',
+        matchState,
+      );
+    }
+
+    final List<String> bodyWithoutPrefix = body
+        .map((String s) => s.substring(_linePrefix.length))
+        .toList(growable: false);
+    final bool hasTailMismatch = IterableZip<String>(<Iterable<String>>[
+      bodyWithoutPrefix.reversed,
+      endsWith.reversed,
+    ]).any((List<String> ss) => ss[0] != ss[1]);
+    if (bodyWithoutPrefix.length < endsWith.length || hasTailMismatch) {
+      return mismatch(
+        'The error message should end with $endsWith.\n'
+        'Actual error(s): $item',
+        matchState,
+      );
+    }
+    return bodyMatcher.matches(
+      bodyWithoutPrefix.sublist(0, bodyWithoutPrefix.length - endsWith.length),
+      matchState,
+    );
+  }
+
+  @override
+  Description describe(Description description) {
+    return description.add('file ${file.path} contains the expected analyze errors.');
+  }
+
+  @override
+  Description describeMismatch(
+    dynamic item,
+    Description mismatchDescription,
+    Map<dynamic, dynamic> matchState,
+    bool verbose,
+  ) {
+    final String? description = matchState[mismatchDescriptionKey] as String?;
+    return description != null
+        ? mismatchDescription.add(description)
+        : mismatchDescription.add('$matchState');
+  }
+}
+
+class _ErrorsInFileMatcher extends Matcher {
+  _ErrorsInFileMatcher(this.file);
+
+  final File file;
+
+  static final RegExp expectationMatcher = RegExp(r'// ERROR: (?<expectations>.+)$');
+
+  static bool mismatch(String mismatchDescription, Map<dynamic, dynamic> matchState) {
+    return _ErrorMatcher.mismatch(mismatchDescription, matchState);
+  }
+
+  List<(int, String)> _expectedErrorMessagesFromFile(Map<dynamic, dynamic> matchState) {
+    final List<(int, String)> returnValue = <(int, String)>[];
+    for (final (int index, String line) in file.readAsLinesSync().indexed) {
+      final List<String> expectations =
+          expectationMatcher.firstMatch(line)?.namedGroup('expectations')?.split(' // ERROR: ') ??
+          <String>[];
+      for (final String expectation in expectations) {
+        returnValue.add((index + 1, expectation));
+      }
+    }
+    return returnValue;
+  }
+
+  @override
+  bool matches(dynamic item, Map<dynamic, dynamic> matchState) {
+    final List<String> actualErrors = item as List<String>;
+    final List<(int, String)> expectedErrors = _expectedErrorMessagesFromFile(matchState);
+    if (expectedErrors.length != actualErrors.length) {
+      return mismatch(
+        'expected ${expectedErrors.length} error(s), got ${actualErrors.length}.\n'
+        'expected lines with errors: ${expectedErrors.map(((int, String) x) => x.$1).toList()}\n'
+        'actual error(s): \n>${actualErrors.join('\n>')}',
+        matchState,
+      );
+    }
+    for (int i = 0; i < actualErrors.length; ++i) {
+      final String actualError = actualErrors[i];
+      final (int lineNumber, String expectedError) = expectedErrors[i];
+      switch (actualError.split(':')) {
+        case [final String _]:
+          return mismatch('No colons (":") found in the error message "$actualError".', matchState);
+        case [final String path, final String line, ...final List<String> rest]:
+          if (!path.endsWith(file.uri.pathSegments.last)) {
+            return mismatch('"$path" does not match the file name of the source file.', matchState);
+          }
+          if (lineNumber.toString() != line) {
+            return mismatch(
+              'could not find the expected error "$expectedError" at line $lineNumber',
+              matchState,
+            );
+          }
+          final String actualMessage = rest.join(':').trimLeft();
+          if (actualMessage != expectedError) {
+            return mismatch(
+              'expected \n"$expectedError"\n at line $lineNumber, got \n"$actualMessage"',
+              matchState,
+            );
+          }
+
+        case _:
+          return mismatch(
+            'failed to recognize a valid path from the error message "$actualError".',
+            matchState,
+          );
+      }
+    }
+    return true;
+  }
+
+  @override
+  Description describe(Description description) => description;
+}