feat: implement MockFile.ReadLinesAsync (#935)

While executing a test a got a hint:

> System.NotImplementedException : This test helper hasn't been implemented yet. They are implemented on an as-needed basis. As it seems like you need it, now would be a great time to send us a pull request over at https://github.com/TestableIO/System.IO.Abstractions. You know, because it's open source and all.

So here is my pull request to add a not implemented feature. 😀

src/TestableIO.System.IO.Abstractions.TestingHelpers/MockFile.Async.cs

@@ -1,6 +1,7 @@
 #if FEATURE_ASYNC_FILE
 
 using System.Collections.Generic;
+using System.Runtime.CompilerServices;
 using System.Text;
 using System.Threading;
 using System.Threading.Tasks;
@@ -23,7 +24,7 @@ public override Task AppendAllLinesAsync(string path, IEnumerable<string> conten
 
         /// <inheritdoc />
         public override Task AppendAllTextAsync(string path, string contents, CancellationToken cancellationToken = default(CancellationToken)) =>
-       AppendAllTextAsync(path, contents, MockFileData.DefaultEncoding, cancellationToken);
+            AppendAllTextAsync(path, contents, MockFileData.DefaultEncoding, cancellationToken);
 
 
         /// <inheritdoc />
@@ -43,7 +44,7 @@ public override Task<byte[]> ReadAllBytesAsync(string path, CancellationToken ca
 
         /// <inheritdoc />
         public override Task<string[]> ReadAllLinesAsync(string path, CancellationToken cancellationToken = default(CancellationToken)) =>
-      ReadAllLinesAsync(path, MockFileData.DefaultEncoding, cancellationToken);
+            ReadAllLinesAsync(path, MockFileData.DefaultEncoding, cancellationToken);
 
         /// <inheritdoc />
 
@@ -55,7 +56,7 @@ public override Task<string[]> ReadAllLinesAsync(string path, Encoding encoding,
 
         /// <inheritdoc />
         public override Task<string> ReadAllTextAsync(string path, CancellationToken cancellationToken) =>
- ReadAllTextAsync(path, MockFileData.DefaultEncoding, cancellationToken);
+            ReadAllTextAsync(path, MockFileData.DefaultEncoding, cancellationToken);
 
 
         /// <inheritdoc />
@@ -67,17 +68,16 @@ public override Task<string> ReadAllTextAsync(string path, Encoding encoding, Ca
 
 #if FEATURE_READ_LINES_ASYNC
         /// <inheritdoc />
-        public override IAsyncEnumerable<string> ReadLinesAsync(string path,
-            CancellationToken cancellationToken = default)
-        {
-            throw CommonExceptions.NotImplemented();
-        }
+        public override IAsyncEnumerable<string> ReadLinesAsync(string path, CancellationToken cancellationToken = default) =>
+            ReadLinesAsync(path, MockFileData.DefaultEncoding, cancellationToken);
 
         /// <inheritdoc />
-        public override IAsyncEnumerable<string> ReadLinesAsync(string path, Encoding encoding,
-            CancellationToken cancellationToken = default)
+        public override async IAsyncEnumerable<string> ReadLinesAsync(string path, Encoding encoding,
+            [EnumeratorCancellation] CancellationToken cancellationToken = default)
         {
-            throw CommonExceptions.NotImplemented();
+            var lines = await ReadAllLinesAsync(path, encoding, cancellationToken);
+            foreach (var line in lines)
+                yield return line;
         }
 #endif
 
@@ -103,7 +103,7 @@ public override Task WriteAllLinesAsync(string path, IEnumerable<string> content
 
         /// <inheritdoc />
         public override Task WriteAllTextAsync(string path, string contents, CancellationToken cancellationToken) =>
-WriteAllTextAsync(path, contents, MockFileData.DefaultEncoding, cancellationToken);
+            WriteAllTextAsync(path, contents, MockFileData.DefaultEncoding, cancellationToken);
 
         /// <inheritdoc />
         public override Task WriteAllTextAsync(string path, string contents, Encoding encoding, CancellationToken cancellationToken)
@@ -115,4 +115,4 @@ public override Task WriteAllTextAsync(string path, string contents, Encoding en
     }
 }
 
-#endif
+#endif

tests/TestableIO.System.IO.Abstractions.TestingHelpers.Tests/MockFileReadAllLinesTests.cs

@@ -1,16 +1,16 @@
 namespace System.IO.Abstractions.TestingHelpers.Tests
 {
     using Collections.Generic;
+    using Collections.Specialized;
+    using Threading;
+    using Threading.Tasks;
 
     using NUnit.Framework;
 
     using Text;
 
     using XFS = MockUnixSupport;
 
-    using System.Threading.Tasks;
-    using System.Threading;
-
     public class MockFileReadAllLinesTests
     {
         [Test]
@@ -63,7 +63,7 @@ public void MockFile_ReadAllLines_NotExistingFile_ThrowsCorrectFileNotFoundExcep
             var mockFileSystem = new MockFileSystem();
 
             var act = new TestDelegate(() =>
-                mockFileSystem.File.ReadAllText(absentFileNameFullPath)
+                mockFileSystem.File.ReadAllLines(absentFileNameFullPath)
             );
 
             var exception = Assert.Catch<FileNotFoundException>(act);
@@ -149,13 +149,95 @@ public void MockFile_ReadAllLinesAsync_NotExistingFile_ThrowsCorrectFileNotFound
             var mockFileSystem = new MockFileSystem();
 
             var act = new AsyncTestDelegate(async () =>
-                await mockFileSystem.File.ReadAllTextAsync(absentFileNameFullPath)
+                await mockFileSystem.File.ReadAllLinesAsync(absentFileNameFullPath)
             );
 
             var exception = Assert.CatchAsync<FileNotFoundException>(act);
             Assert.That(exception.FileName, Is.EqualTo(absentFileNameFullPath));
             Assert.That(exception.Message, Is.EqualTo("Could not find file '" + absentFileNameFullPath + "'."));
         }
+
+#if FEATURE_READ_LINES_ASYNC
+        [Test]
+        public async Task MockFile_ReadLinesAsync_ShouldReturnOriginalTextData()
+        {
+            // Arrange
+            var fileSystem = new MockFileSystem(new Dictionary<string, MockFileData>
+            {
+                { XFS.Path(@"c:\something\demo.txt"), new MockFileData("Demo\r\ntext\ncontent\rvalue") },
+                { XFS.Path(@"c:\something\other.gif"), new MockFileData(new byte[] { 0x21, 0x58, 0x3f, 0xa9 }) }
+            });
+
+            var file = new MockFile(fileSystem);
+
+            // Act
+            var enumerable = file.ReadLinesAsync(XFS.Path(@"c:\something\demo.txt"));
+            StringCollection result = new();
+            await foreach (var line in enumerable)
+                result.Add(line);
+
+            // Assert
+            CollectionAssert.AreEqual(
+                new[] { "Demo", "text", "content", "value" },
+                result);
+        }
+
+        [Test]
+        public async Task MockFile_ReadLinesAsync_ShouldReturnOriginalDataWithCustomEncoding()
+        {
+            // Arrange
+            string text = "Hello\r\nthere\rBob\nBob!";
+            var encodedText = Encoding.BigEndianUnicode.GetBytes(text);
+            var fileSystem = new MockFileSystem(new Dictionary<string, MockFileData>
+            {
+                { XFS.Path(@"c:\something\demo.txt"), new MockFileData(encodedText) }
+            });
+
+            var file = new MockFile(fileSystem);
+
+            // Act
+            var enumerable = file.ReadLinesAsync(XFS.Path(@"c:\something\demo.txt"), Encoding.BigEndianUnicode);
+            StringCollection result = new();
+            await foreach (var line in enumerable)
+                result.Add(line);
+
+            // Assert
+            CollectionAssert.AreEqual(
+                new[] { "Hello", "there", "Bob", "Bob!" },
+                result);
+        }
+
+        [Test]
+        public void MockFile_ReadLinesAsync_ShouldThrowOperationCanceledExceptionIfCanceled()
+        {
+            var fileSystem = new MockFileSystem();
+
+            AsyncTestDelegate action = async () =>
+            {
+                var enumerable = fileSystem.File.ReadLinesAsync(@"C:\a.txt", new CancellationToken(canceled: true));
+                await foreach (var line in enumerable);
+            };
+
+            Assert.ThrowsAsync<OperationCanceledException>(action);
+        }
+
+        [Test]
+        public void MockFile_ReadLinesAsync_NotExistingFile_ThrowsCorrectFileNotFoundException()
+        {
+            var absentFileNameFullPath = XFS.Path(@"c:\you surely don't have such file.hope-so");
+            var mockFileSystem = new MockFileSystem();
+
+            AsyncTestDelegate action = async () =>
+            {
+                var enumerable = mockFileSystem.File.ReadLinesAsync(absentFileNameFullPath);
+                await foreach (var line in enumerable) ;
+            };
+
+            var exception = Assert.CatchAsync<FileNotFoundException>(action);
+            Assert.That(exception.FileName, Is.EqualTo(absentFileNameFullPath));
+            Assert.That(exception.Message, Is.EqualTo("Could not find file '" + absentFileNameFullPath + "'."));
+        }
+#endif
 #endif
     }
-}
+}