Apply suggestions from code review.

Use helpers for temp files; improve code formatting.

Co-authored-by: Adam Sitnik <adam.sitnik@gmail.com>

src/libraries/System.IO/tests/StreamReader/StreamReaderTests.cs

@@ -131,30 +131,15 @@ public async Task ReadToEndAsync_WithCanceledCancellationToken()
         [Fact]
         public async Task ReadToEndAsync_WithCancellation()
         {
-            var path = Path.GetTempFileName();
-            try
-            {
-                // create large (~100MB) file
-                using (var writer = new StreamWriter(path))
-                {
-                    for (var i = 0; i < 1_000_000; i++)
-                        writer.WriteLine("A very large file used for testing StreamReader cancellation. 0123456789012345678901234567890123456789.");
-                }
-
-                using var reader = File.OpenText(path);
-                using var cts = new CancellationTokenSource(TimeSpan.FromMilliseconds(50));
-                await Assert.ThrowsAnyAsync<OperationCanceledException>(async () => await reader.ReadToEndAsync(cts.Token));
-            }
-            finally
-            {
-                try
-                {
-                    File.Delete(path);
-                }
-                catch (Exception)
-                {
-                }
-            }
+            string path = GetTestFilePath();
+
+            // create large (~100MB) file
+            File.WriteAllLines(path, Enumerable.Repeat("A very large file used for testing StreamReader cancellation. 0123456789012345678901234567890123456789.", 1_000_000));
+
+            using StreamReader reader = File.OpenText(path);
+            using CancellationTokenSource cts = new (TimeSpan.FromMilliseconds(50));
+
+            await Assert.ThrowsAnyAsync<OperationCanceledException>(async () => await reader.ReadToEndAsync(cts.Token));
         }
 
         [Fact]

src/libraries/System.IO/tests/TextReader/TextReaderTests.cs

@@ -69,7 +69,10 @@ public async Task ReadToEndAsync_WithCanceledCancellationToken()
             using var tr = new CharArrayTextReader(TestDataProvider.LargeData);
             using var cts = new CancellationTokenSource();
             cts.Cancel();
-            await Assert.ThrowsAnyAsync<OperationCanceledException>(async () => await tr.ReadToEndAsync(cts.Token));
+            CancellationToken token = cts.Token;
+
+            TaskCanceledException ex = await Assert.ThrowsAsync<OperationCanceledException>(async () => await tr.ReadToEndAsync(token));
+            Assert.Equal(token, ex.CancellationToken);
         }
 
         [Fact]

src/libraries/System.Private.CoreLib/src/System/IO/StreamReader.cs

@@ -929,8 +929,7 @@ private int ReadBuffer(Span<char> userBuffer, out bool readToUserBuffer)
             return sb.ToString();
         }
 
-        public override Task<string> ReadToEndAsync() =>
-            ReadToEndAsync(default);
+        public override Task<string> ReadToEndAsync() => ReadToEndAsync(default);
 
         public override Task<string> ReadToEndAsync(CancellationToken cancellationToken)
         {

src/libraries/System.Private.CoreLib/src/System/IO/TextReader.cs

@@ -212,8 +212,7 @@ public virtual int ReadBlock(Span<char> buffer)
             Task<string?>.Factory.StartNew(static state => ((TextReader)state!).ReadLine(), this,
                 cancellationToken, TaskCreationOptions.DenyChildAttach, TaskScheduler.Default);
 
-        public virtual Task<string> ReadToEndAsync() =>
-            ReadToEndAsync(default);
+        public virtual Task<string> ReadToEndAsync() => ReadToEndAsync(default);
 
         public virtual async Task<string> ReadToEndAsync(CancellationToken cancellationToken)
         {
@@ -377,13 +376,15 @@ protected override void Dispose(bool disposing)
             public override Task<string?> ReadLineAsync() => Task.FromResult(ReadLine());
 
             [MethodImpl(MethodImplOptions.Synchronized)]
-            public override ValueTask<string?> ReadLineAsync(CancellationToken cancellationToken) => cancellationToken.IsCancellationRequested ? ValueTask.FromCanceled<string?>(cancellationToken) : new ValueTask<string?>(ReadLine());
+            public override ValueTask<string?> ReadLineAsync(CancellationToken cancellationToken)
+                => cancellationToken.IsCancellationRequested ? ValueTask.FromCanceled<string?>(cancellationToken) : new ValueTask<string?>(ReadLine());
 
             [MethodImpl(MethodImplOptions.Synchronized)]
             public override Task<string> ReadToEndAsync() => Task.FromResult(ReadToEnd());
 
             [MethodImpl(MethodImplOptions.Synchronized)]
-            public override Task<string> ReadToEndAsync(CancellationToken cancellationToken) => cancellationToken.IsCancellationRequested ? Task.FromCanceled<string>(cancellationToken) : Task.FromResult(ReadToEnd());
+            public override Task<string> ReadToEndAsync(CancellationToken cancellationToken)
+                => cancellationToken.IsCancellationRequested ? Task.FromCanceled<string>(cancellationToken) : Task.FromResult(ReadToEnd());
 
             [MethodImpl(MethodImplOptions.Synchronized)]
             public override Task<int> ReadBlockAsync(char[] buffer, int index, int count)