.

src/Verify/Compare/SharedSettings.cs

@@ -2,8 +2,8 @@
 
 public static partial class VerifierSettings
 {
-    static Dictionary<string, StringCompare> stringComparers = [];
-    static Dictionary<string, StreamCompare> streamComparers = [];
+    static IDictionary<string, StringCompare> stringComparers = new Dictionary<string, StringCompare>();
+    static IDictionary<string, StreamCompare> streamComparers = new Dictionary<string, StreamCompare>();
     static StringCompare? defaultStringComparer;
 
     internal static bool TryGetStreamComparer(string extension, [NotNullWhen(true)] out StreamCompare? comparer) =>

src/Verify/Counter.cs

@@ -2,6 +2,17 @@
 
 public partial class Counter
 {
+    internal static void FirstRun()
+    {
+#if NET8_0_OR_GREATER
+        globalNamedDates = globalNamedDates.ToFrozenDictionary();
+        globalNamedDateTimes = globalNamedDateTimes.ToFrozenDictionary();
+        globalNamedDateTimeOffsets = globalNamedDateTimeOffsets.ToFrozenDictionary();
+        globalNamedGuids = globalNamedGuids.ToFrozenDictionary();
+        globalNamedTimes = globalNamedTimes.ToFrozenDictionary();
+#endif
+    }
+
 #if NET6_0_OR_GREATER
     Dictionary<Date, string> namedDates;
     Dictionary<Time, string> namedTimes;

src/Verify/Counter_Date.cs

@@ -4,9 +4,8 @@ namespace VerifyTests;
 public partial class Counter
 {
     ConcurrentDictionary<Date, (int intValue, string stringValue)> dateCache = [];
-    static Dictionary<Date, string> globalNamedDates = [];
+    static IDictionary<Date, string> globalNamedDates = new Dictionary<Date, string>();
     int currentDate;
-
     internal static void AddNamed(Date value, string name)
     {
         InnerVerifier.ThrowIfVerifyHasBeenRun();

src/Verify/Counter_DateTime.cs

@@ -3,7 +3,7 @@
 public partial class Counter
 {
     ConcurrentDictionary<DateTime, (int intValue, string stringValue)> dateTimeCache = new(new DateTimeComparer());
-    static Dictionary<DateTime, string> globalNamedDateTimes = [];
+    static IDictionary<DateTime, string> globalNamedDateTimes = new Dictionary<DateTime, string>();
 
     class DateTimeComparer : IEqualityComparer<DateTime>
     {

src/Verify/Counter_DateTimeOffset.cs

@@ -3,7 +3,7 @@
 public partial class Counter
 {
     ConcurrentDictionary<DateTimeOffset, (int intValue, string stringValue)> dateTimeOffsetCache = new(new DateTimeOffsetComparer());
-    static Dictionary<DateTimeOffset, string> globalNamedDateTimeOffsets = [];
+    static IDictionary<DateTimeOffset, string> globalNamedDateTimeOffsets = new Dictionary<DateTimeOffset, string>();
 
     class DateTimeOffsetComparer :
         IEqualityComparer<DateTimeOffset>

src/Verify/Counter_Guid.cs

@@ -3,7 +3,7 @@
 public partial class Counter
 {
     ConcurrentDictionary<Guid, (int intValue, string stringValue)> guidCache = [];
-    static Dictionary<Guid, string> globalNamedGuids = [];
+    static IDictionary<Guid, string> globalNamedGuids = new Dictionary<Guid, string>();
     int currentGuid;
 
     public int Next(Guid input) =>

src/Verify/Counter_Time.cs

@@ -4,7 +4,7 @@ namespace VerifyTests;
 public partial class Counter
 {
     ConcurrentDictionary<Time, (int intValue, string stringValue)> timeCache = [];
-    static Dictionary<Time, string> globalNamedTimes = [];
+    static IDictionary<Time, string> globalNamedTimes = new Dictionary<Time, string>();
     int currentTime;
 
     internal static void AddNamed(Time time, string name)

src/Verify/Naming/VerifierSettings.cs

@@ -4,7 +4,7 @@ public static partial class VerifierSettings
 {
     internal static Namer SharedNamer = new();
 
-    static Dictionary<Type, Func<object, string>> parameterToNameLookup = new()
+    static IDictionary<Type, Func<object, string>> parameterToNameLookup = new Dictionary<Type, Func<object, string>>
     {
         {
             typeof(bool), _ => ((bool) _).ToString(Culture.InvariantCulture)

src/Verify/Serialization/Scrubbers/VerifierSettings_ExtensionMappedGlobalScrubbers.cs

@@ -2,7 +2,7 @@
 
 public static partial class VerifierSettings
 {
-    internal static Dictionary<string, List<Action<StringBuilder, Counter>>> ExtensionMappedGlobalScrubbers = [];
+    internal static IDictionary<string, List<Action<StringBuilder, Counter>>> ExtensionMappedGlobalScrubbers =  new Dictionary<string, List<Action<StringBuilder, Counter>>>();
 
     /// <summary>
     /// Modify the resulting test content using custom code.

src/Verify/Serialization/VerifierSettings.cs

@@ -33,7 +33,7 @@ public static bool TryGetToString(
         return typeToString.TryGetValue(target.GetType(), out toString);
     }
 
-    static Dictionary<Type, Func<object, IReadOnlyDictionary<string, object>, AsStringResult>> typeToString = new()
+    static IDictionary<Type, Func<object, IReadOnlyDictionary<string, object>, AsStringResult>> typeToString = new Dictionary<Type, Func<object, IReadOnlyDictionary<string, object>, AsStringResult>>
     {
         #region typeToStringMapping
 
@@ -135,7 +135,7 @@ public static void TreatAsString<T>(AsString<T>? toString = null)
 
     internal static void Reset()
     {
-        InnerVerifier.verifyHasBeenRun = false;
+        InnerVerifier.verifyHasBeenRun = 0;
         DateCountingEnabled = true;
         StrictJson = false;
         scrubProjectDir = true;

src/Verify/Serialization/VerifierSettings_MemberConverter.cs

@@ -2,7 +2,7 @@
 
 public static partial class VerifierSettings
 {
-    static Dictionary<Type, Dictionary<string, ConvertTargetMember>> membersConverters = [];
+    static IDictionary<Type, Dictionary<string, ConvertTargetMember>> membersConverters = new Dictionary<Type, Dictionary<string, ConvertTargetMember>>();
 
     internal static ConvertTargetMember? GetMemberConverter(MemberInfo member) =>
         GetMemberConverter(member.DeclaringType, member.Name);

src/Verify/Splitters/Settings_Extension.cs

@@ -2,7 +2,7 @@
 
 public static partial class VerifierSettings
 {
-    static Dictionary<string, AsyncConversion<Stream>> extensionConverters = [];
+    static IDictionary<string, AsyncConversion<Stream>> extensionConverters = new Dictionary<string, AsyncConversion<Stream>>();
 
     internal static bool TryGetExtensionConverter(string extension, [NotNullWhen(true)] out AsyncConversion<Stream>? converter) =>
         extensionConverters.TryGetValue(extension, out converter);

src/Verify/Verifier/InnerVerifier.cs

@@ -11,12 +11,12 @@ public partial class InnerVerifier :
     GetIndexedFileNames getIndexedFileNames = null!;
     IEnumerable<string> verifiedFiles = null!;
     Counter counter;
-    internal static bool verifyHasBeenRun;
+    internal static int verifyHasBeenRun;
 
     [MethodImpl(MethodImplOptions.NoInlining)]
     public static void ThrowIfVerifyHasBeenRun()
     {
-        if (!verifyHasBeenRun)
+        if (verifyHasBeenRun == 0)
         {
             return;
         }
@@ -38,7 +38,7 @@ public InnerVerifier(
         Guard.AgainstEmpty(sourceFile);
         Guard.AgainstEmpty(typeName);
         Guard.AgainstEmpty(methodName);
-        verifyHasBeenRun = true;
+        FirstRun();
         VerifierSettings.RunBeforeCallbacks();
         this.settings = settings;
 
@@ -63,6 +63,15 @@ public InnerVerifier(
         }
     }
 
+    static void FirstRun()
+    {
+        if (Interlocked.Exchange(ref verifyHasBeenRun, 1) == 0)
+        {
+            VerifierSettings.FirstRun();
+            Counter.FirstRun();
+        }
+    }
+
     /// <summary>
     /// Initialize a new instance of the <see cref="InnerVerifier" /> class for verifying the entire file (not just a specific type)
     /// </summary>

src/Verify/VerifierSettings.cs

@@ -7,6 +7,19 @@ public static partial class VerifierSettings
     public static void OmitContentFromException() =>
         omitContentFromException = true;
 
+    internal static void FirstRun()
+    {
+#if NET8_0_OR_GREATER
+        stringComparers = stringComparers.ToFrozenDictionary();
+        streamComparers = streamComparers.ToFrozenDictionary();
+        parameterToNameLookup = parameterToNameLookup.ToFrozenDictionary();
+        ExtensionMappedGlobalScrubbers = ExtensionMappedGlobalScrubbers.ToFrozenDictionary();
+        typeToString = typeToString.ToFrozenDictionary();
+        membersConverters = membersConverters.ToFrozenDictionary();
+        extensionConverters = extensionConverters.ToFrozenDictionary();
+#endif
+    }
+
     /// <summary>
     /// Automatically accept the results of all tests.
     /// </summary>