test: don't create spurious files during testing

Chickensoft.Log.Tests/test/src/FileWriterTest.cs

@@ -6,24 +6,28 @@ namespace Chickensoft.Log.Tests;
 
 public class FileWriterStreamTester : IDisposable {
   private bool _isDisposed;
-  private readonly MemoryStream _memoryStream;
+  private readonly MemoryStream _openingMemoryStream;
+  private readonly MemoryStream _appendingMemoryStream;
 
   public FileWriterStreamTester(
     string filename = FileWriter.DEFAULT_FILE_NAME
   ) {
-    _memoryStream = new MemoryStream();
+    _openingMemoryStream = new MemoryStream();
+    _appendingMemoryStream = new MemoryStream();
 
     FileWriter.AppendText = fileName => new StreamWriter(
-      _memoryStream,
+      _appendingMemoryStream,
       System.Text.Encoding.UTF8,
       bufferSize: 1024,
       leaveOpen: true
     );
+
+    FileWriter.CreateFile = fileName => _openingMemoryStream;
   }
 
   public string GetString() {
-    _memoryStream.Position = 0;
-    using var reader = new StreamReader(_memoryStream);
+    _appendingMemoryStream.Position = 0;
+    using var reader = new StreamReader(_appendingMemoryStream);
     return reader.ReadToEnd();
   }
 
@@ -34,7 +38,9 @@ public void Dispose() {
     _isDisposed = true;
 
     FileWriter.AppendText = FileWriter.AppendTextDefault;
-    _memoryStream.Dispose();
+    FileWriter.CreateFile = FileWriter.CreateFileDefault;
+    _openingMemoryStream.Dispose();
+    _appendingMemoryStream.Dispose();
   }
 }
 

Chickensoft.Log/src/FileWriter.cs

@@ -8,12 +8,17 @@ namespace Chickensoft.Log;
 /// to a file.
 /// </summary>
 public sealed class FileWriter : ILogWriter {
-  internal delegate StreamWriter AppendTextDelegate(string text);
+  internal delegate StreamWriter AppendTextDelegate(string path);
   internal static AppendTextDelegate AppendTextDefault { get; } =
     File.AppendText;
   internal static AppendTextDelegate AppendText { get; set; } =
     AppendTextDefault;
 
+  internal delegate Stream CreateFileDelegate(string path);
+  internal static CreateFileDelegate CreateFileDefault { get; } = File.Create;
+  internal static CreateFileDelegate CreateFile { get; set; } =
+    CreateFileDefault;
+
   // protect static members from simultaneous thread access
   private static readonly object _singletonLock = new();
   // Implemented as a pseudo-singleton to enforce one truncation per file per
@@ -126,7 +131,7 @@ private FileWriter(string fileName) {
     FileName = fileName;
     lock (_writingLock) {
       // Clear the file
-      using var sw = new StreamWriter(FileName);
+      using var sw = CreateFile(FileName);
     }
   }