diff --git a/packages/file/CHANGELOG.md b/packages/file/CHANGELOG.md
index b2c3ae7..cc5c305 100644
--- a/packages/file/CHANGELOG.md
+++ b/packages/file/CHANGELOG.md
@@ -6,6 +6,11 @@
   in the file as the start of a new, empty line.
 * `RecordingFile.readAsLine()`/`readAsLinesSync()` now always record a final
   newline.
+* `MemoryFile.flush()` now returns `Future<void>` instead of `Future<dynamic>`.
+* Fixed incorrect formatting in `NoMatchingInvocationError.toString()`.
+* Fixed a lot of test flakiness.
+* Enabled more tests.
+* Internal cleanup.
 
 #### 5.2.0
 
diff --git a/packages/file/test/common_tests.dart b/packages/file/test/common_tests.dart
index b99f3aa..b5ad188 100644
--- a/packages/file/test/common_tests.dart
+++ b/packages/file/test/common_tests.dart
@@ -1567,12 +1567,12 @@
 
       group('lastAccessed', () {
         test('isNowForNewlyCreatedFile', () {
-          DateTime before = floor();
+          DateTime before = downstairs();
           File f = fs.file(ns('/foo'))..createSync();
           DateTime after = ceil();
           DateTime accessed = f.lastAccessedSync();
-          expect(before, isSameOrBefore(accessed));
-          expect(after, isSameOrAfter(accessed));
+          expect(accessed, isSameOrAfter(before));
+          expect(accessed, isSameOrBefore(after));
         });
 
         test('throwsIfDoesntExist', () {
@@ -1589,13 +1589,13 @@
         });
 
         test('succeedsIfExistsAsLinkToFile', () {
-          DateTime before = floor();
+          DateTime before = downstairs();
           fs.file(ns('/foo')).createSync();
           fs.link(ns('/bar')).createSync(ns('/foo'));
           DateTime after = ceil();
           DateTime accessed = fs.file(ns('/bar')).lastAccessedSync();
-          expect(before, isSameOrBefore(accessed));
-          expect(after, isSameOrAfter(accessed));
+          expect(accessed, isSameOrAfter(before));
+          expect(accessed, isSameOrBefore(after));
         });
       });
 
@@ -1631,12 +1631,12 @@
 
       group('lastModified', () {
         test('isNowForNewlyCreatedFile', () {
-          DateTime before = floor();
+          DateTime before = downstairs();
           File f = fs.file(ns('/foo'))..createSync();
           DateTime after = ceil();
           DateTime modified = f.lastModifiedSync();
-          expect(before, isSameOrBefore(modified));
-          expect(after, isSameOrAfter(modified));
+          expect(modified, isSameOrAfter(before));
+          expect(modified, isSameOrBefore(after));
         });
 
         test('throwsIfDoesntExist', () {
@@ -1653,13 +1653,13 @@
         });
 
         test('succeedsIfExistsAsLinkToFile', () {
-          DateTime before = floor();
+          DateTime before = downstairs();
           fs.file(ns('/foo')).createSync();
           fs.link(ns('/bar')).createSync(ns('/foo'));
           DateTime after = ceil();
           DateTime modified = fs.file(ns('/bar')).lastModifiedSync();
-          expect(before, isSameOrBefore(modified));
-          expect(after, isSameOrAfter(modified));
+          expect(modified, isSameOrAfter(before));
+          expect(modified, isSameOrBefore(after));
         });
       });
 
diff --git a/packages/file/test/utils.dart b/packages/file/test/utils.dart
index 2d7a6db..aebad3e 100644
--- a/packages/file/test/utils.dart
+++ b/packages/file/test/utils.dart
@@ -5,6 +5,8 @@
 import 'package:meta/meta.dart';
 import 'package:test/test.dart';
 
+const Duration _oneSecond = Duration(seconds: 1);
+
 /// Returns a [DateTime] with an exact second-precision by removing the
 /// milliseconds and microseconds from the specified [time].
 ///
@@ -17,17 +19,23 @@
   ));
 }
 
-/// Returns a [DateTime] with an exact second precision by adding just enough
-/// milliseconds and microseconds to the specified [time] to reach the next
-/// second.
+/// Returns a [DateTime] with an exact second precision, rounding up to the
+/// nearest second if necessary.
 ///
 /// If [time] is not specified, it will default to the current time.
 DateTime ceil([DateTime time]) {
   time ??= DateTime.now();
   int microseconds = (1000 * time.millisecond) + time.microsecond;
-  return time.add(Duration(microseconds: 1000000 - microseconds));
+  return (microseconds == 0)
+      ? time
+      // Add just enough milliseconds and microseconds to reach the next second.
+      : time.add(Duration(microseconds: 1000000 - microseconds));
 }
 
+/// Returns 1 second before the [floor] of the specified [DateTime].
+// TODO(jamesderlin): Remove this and use [floor], https://github.com/dart-lang/sdk/issues/42444
+DateTime downstairs([DateTime time]) => floor(time).subtract(_oneSecond);
+
 /// Successfully matches against a [DateTime] that is the same moment or before
 /// the specified [time].
 Matcher isSameOrBefore(DateTime time) => _IsSameOrBefore(time);
diff --git a/packages/file/test/utils_test.dart b/packages/file/test/utils_test.dart
index 2e45896..75293bf 100644
--- a/packages/file/test/utils_test.dart
+++ b/packages/file/test/utils_test.dart
@@ -27,9 +27,17 @@
 
   test('floorAndCeilWorkWithExactSecondDateTime', () {
     DateTime time = DateTime.parse('1999-12-31 23:59:59');
-    int lower = time.difference(floor(time)).inMicroseconds;
-    int upper = ceil(time).difference(time).inMicroseconds;
-    expect(lower, 0);
-    expect(upper, lessThanOrEqualTo(1000000));
+    DateTime lower = floor(time);
+    DateTime upper = ceil(time);
+    expect(lower, time);
+    expect(upper, time);
+  });
+
+  test('floorAndCeilWorkWithInexactSecondDateTime', () {
+    DateTime time = DateTime.parse('1999-12-31 23:59:59.500');
+    DateTime lower = floor(time);
+    DateTime upper = ceil(time);
+    Duration difference = upper.difference(lower);
+    expect(difference.inMicroseconds, 1000000);
   });
 }