Add MiniPdf.ClearRegisteredFonts

documents/README.nuget.md

@@ -91,6 +91,9 @@ MiniPdf.RegisterFont("NotoSansSC", File.ReadAllBytes("Fonts/NotoSansSC-Regular.t
 MiniPdf.ConvertToPdf("report.docx", "report.pdf");
 ```
 
+Registrations are process-wide. `MiniPdf.ClearRegisteredFonts()` removes them when
+the same process needs a different font set for a later conversion.
+
 ## Command Line
 
 Install the .NET global tool:

src/MiniPdf/MiniPdf.cs

@@ -128,6 +128,16 @@ public static void RegisterFont(string name, byte[] fontData)
             _registeredFonts.Add((name, fontData));
     }
 
+    /// <summary>
+    /// Removes all fonts registered with <see cref="RegisterFont"/>.
+    /// Registrations are process-wide; clear them before registering a different font set.
+    /// </summary>
+    public static void ClearRegisteredFonts()
+    {
+        lock (_registeredFonts)
+            _registeredFonts.Clear();
+    }
+
     /// <summary>
     /// Returns a snapshot of all registered fonts.
     /// </summary>

tests/MiniPdf.Tests/RegisteredFontTests.cs

@@ -0,0 +1,70 @@
+namespace MiniSoftware.Tests;
+
+/// <summary>
+/// Runs registered-font tests apart from other collections. Registrations are process-wide,
+/// so conversions running in parallel would otherwise read the fonts these tests register.
+/// </summary>
+[CollectionDefinition(Name, DisableParallelization = true)]
+public class RegisteredFontCollection
+{
+    public const string Name = "Registered fonts";
+}
+
+[Collection(RegisteredFontCollection.Name)]
+public class RegisteredFontTests : IDisposable
+{
+    /// <summary>
+    /// Starts each test with no registered fonts.
+    /// </summary>
+    public RegisteredFontTests() => MiniPdf.ClearRegisteredFonts();
+
+    /// <summary>
+    /// Clears the fonts a test registered so the next test starts from an empty list.
+    /// </summary>
+    public void Dispose() => MiniPdf.ClearRegisteredFonts();
+
+    /// <summary>
+    /// Clearing removes every registration, including repeated registrations of the same name.
+    /// </summary>
+    [Fact]
+    public void ClearRegisteredFonts_RemovesAllRegistrations()
+    {
+        MiniPdf.RegisterFont("First", new byte[] { 1 });
+        MiniPdf.RegisterFont("Second", new byte[] { 2 });
+        MiniPdf.RegisterFont("First", new byte[] { 3 });
+        Assert.Equal(3, MiniPdf.GetRegisteredFonts().Count);
+
+        MiniPdf.ClearRegisteredFonts();
+
+        Assert.Empty(MiniPdf.GetRegisteredFonts());
+    }
+
+    /// <summary>
+    /// A host can swap font sets between conversions by clearing and registering again.
+    /// </summary>
+    [Fact]
+    public void ClearRegisteredFonts_AllowsRegisteringADifferentFontSet()
+    {
+        MiniPdf.RegisterFont("NotoSansTC", new byte[] { 1 });
+
+        MiniPdf.ClearRegisteredFonts();
+        MiniPdf.RegisterFont("NotoSansJP", new byte[] { 2 });
+
+        var registered = Assert.Single(MiniPdf.GetRegisteredFonts());
+        Assert.Equal("NotoSansJP", registered.Name);
+    }
+
+    /// <summary>
+    /// A snapshot taken before clearing, such as the one a conversion in progress reads, is not changed.
+    /// </summary>
+    [Fact]
+    public void ClearRegisteredFonts_DoesNotChangeEarlierSnapshot()
+    {
+        MiniPdf.RegisterFont("NotoSansTC", new byte[] { 1 });
+        var snapshot = MiniPdf.GetRegisteredFonts();
+
+        MiniPdf.ClearRegisteredFonts();
+
+        Assert.Equal("NotoSansTC", Assert.Single(snapshot).Name);
+    }
+}