.

src/Verify/Extensions.cs

@@ -3,7 +3,7 @@
 static class Extensions
 {
     public static string Extension(this FileStream file) =>
-        FileExtensions.GetExtension(file.Name);
+        Path.GetExtension(file.Name);
 
     public static bool ContainsNewline(this CharSpan span) =>
         span.IndexOfAny('\r', '\n') != -1;

src/Verify/FilePair.cs

@@ -5,5 +5,5 @@ public readonly struct FilePair(string extension, string receivedPath, string ve
     public string Extension { get; } = extension;
     public string ReceivedPath { get; } = receivedPath;
     public string VerifiedPath { get; } = verifiedPath;
-    public bool IsText { get; } = FileExtensions.IsText(extension);
+    public bool IsText { get; } = FileExtensions.IsTextExtension(extension);
 }

src/Verify/Guard.cs

@@ -140,9 +140,9 @@ public static void AgainstBadExtension(string value, [CallerArgumentExpression("
     {
         AgainstNullOrEmpty(value, argumentName);
 
-        if (value.StartsWith('.'))
+        if (!value.StartsWith('.'))
         {
-            throw new ArgumentException("Must not start with a period ('.').", argumentName);
+            throw new ArgumentException("Must start with a period ('.').", argumentName);
         }
     }
 }

src/Verify/Splitters/Settings_Extension.cs

@@ -25,8 +25,7 @@ public static void RegisterFileConverter(
         AsyncConversion<Stream> conversion)
     {
         InnerVerifier.ThrowIfVerifyHasBeenRun();
-        Guard.AgainstBadExtension(fromExtension);
-        if (FileExtensions.IsText(fromExtension))
+        if (FileExtensions.IsTextExtension(fromExtension))
         {
             throw new("RegisterFileConverter is only supported for non-text extensions");
         }

src/Verify/Splitters/Settings_FileAppender.cs

@@ -40,7 +40,7 @@ public void AppendContentAsFile(StringBuilder content, string extension = "txt",
 
     public void AppendContentAsFile(byte[] content, string extension = "txt", string? name = null)
     {
-        if (FileExtensions.IsText(extension))
+        if (FileExtensions.IsTextExtension(extension))
         {
             appendedFiles.Add(new(extension, Encoding.UTF8.GetString(content), name));
         }
@@ -62,7 +62,7 @@ public void AppendFile(FileStream stream, string? name = null) =>
     public void AppendFile(Stream stream, string extension = "txt", string? name = null)
     {
         stream.MoveToStart();
-        if (FileExtensions.IsText(extension))
+        if (FileExtensions.IsTextExtension(extension))
         {
             using var reader = new StreamReader(stream, Encoding.UTF8);
             appendedFiles.Add(new(extension, reader.ReadToEnd(), name));

src/Verify/Target.cs

@@ -38,9 +38,7 @@ internal bool TryGetStringBuilder([NotNullWhen(true)] out StringBuilder? value)
 
     public Target(string extension, Stream data, string? name = null)
     {
-        Guard.AgainstBadExtension(extension);
-
-        if (FileExtensions.IsText(extension))
+        if (FileExtensions.IsTextExtension(extension))
         {
             throw new("Dont pass a stream for text. Instead use `Target(string extension, string data)` or `Target(string extension, StringBuilder data, string? name)`.");
         }
@@ -53,9 +51,8 @@ public Target(string extension, Stream data, string? name = null)
 
     public Target(string extension, StringBuilder data, string? name = null)
     {
-        Guard.AgainstBadExtension(extension);
         Guard.AgainstEmpty(name);
-        if (!FileExtensions.IsText(extension))
+        if (!FileExtensions.IsTextExtension(extension))
         {
             throw new("Dont pass a text for a binary extension. Instead use `Target(string extension, Stream data, string? name)`.");
         }
@@ -68,9 +65,8 @@ public Target(string extension, StringBuilder data, string? name = null)
 
     public Target(string extension, string data, string? name = null)
     {
-        Guard.AgainstBadExtension(extension);
         Guard.AgainstEmpty(name, nameof(name));
-        if (!FileExtensions.IsText(extension))
+        if (!FileExtensions.IsTextExtension(extension))
         {
             throw new("Dont pass a text for a binary extension. Instead use `Target(string extension, Stream data, string? name)`.");
         }

src/Verify/Verifier/InnerVerifier.cs

@@ -82,7 +82,7 @@ public InnerVerifier(string sourceFile, VerifySettings settings)
         ValidatePrefix(settings, directory);
 
         var withoutExtension = Path.GetFileNameWithoutExtension(sourceFile);
-        verifiedFiles = [Path.Combine(directory, $"{withoutExtension}.verified.{FileExtensions.GetExtension(sourceFile)}")];
+        verifiedFiles = [Path.Combine(directory, $"{withoutExtension}.verified{Path.GetExtension(sourceFile)}")];
 
         getFileNames = target =>
             new(

src/Verify/Verifier/InnerVerifier_Directory.cs

@@ -115,7 +115,7 @@ static async Task<Target> TargetFromFile(string path, string relativePath, FileS
                 relativePath);
         }
 
-        if (FileExtensions.IsText(extension))
+        if (FileExtensions.IsTextExtension(extension))
         {
             using var stream = openStream();
             var builder = await stream.ReadStringBuilderWithFixedLines();

src/Verify/Verifier/InnerVerifier_Stream.cs

@@ -111,7 +111,7 @@ public async Task<VerifyResult> VerifyStream(Stream? stream, string extension, o
 
     static async Task<Target> GetTarget(Stream stream, string extension)
     {
-        if (FileExtensions.IsText(extension))
+        if (FileExtensions.IsTextExtension(extension))
         {
             return new(extension, await stream.ReadStringBuilderWithFixedLines());
         }