Add support for building immutable collection objects

src/Atc.Test/Customizations/ImmutableObjectCustomization.cs

@@ -0,0 +1,79 @@
+#if NET5_0_OR_GREATER
+using System.Collections.Immutable;
+
+namespace Atc.Test.Customizations;
+
+[AutoRegister]
+public class ImmutableObjectCustomization : ICustomization
+{
+    public void Customize(IFixture fixture)
+    {
+        fixture.Customizations.Add(
+            new ImmutableObjectBuilder(
+                typeof(ImmutableArray<>),
+                typeof(List<>),
+                o => ImmutableArray.ToImmutableArray(o)));
+
+        fixture.Customizations.Add(
+            new ImmutableObjectBuilder(
+                typeof(ImmutableList<>),
+                typeof(List<>),
+                o => ImmutableList.ToImmutableList(o)));
+
+        fixture.Customizations.Add(
+            new ImmutableObjectBuilder(
+                typeof(ImmutableDictionary<,>),
+                typeof(Dictionary<,>),
+                o => ImmutableDictionary.ToImmutableDictionary(o)));
+
+        fixture.Customizations.Add(
+            new ImmutableObjectBuilder(
+                typeof(ImmutableHashSet<>),
+                typeof(HashSet<>),
+                o => ImmutableHashSet.ToImmutableHashSet(o)));
+
+        fixture.Customizations.Add(
+            new ImmutableObjectBuilder(
+                typeof(ImmutableSortedSet<>),
+                typeof(SortedSet<>),
+                o => ImmutableSortedSet.ToImmutableSortedSet(o)));
+
+        fixture.Customizations.Add(
+            new ImmutableObjectBuilder(
+                typeof(ImmutableSortedDictionary<,>),
+                typeof(SortedDictionary<,>),
+                o => ImmutableSortedDictionary.ToImmutableSortedDictionary(o)));
+    }
+
+    private sealed class ImmutableObjectBuilder(
+        Type immutableType,
+        Type underlyingType,
+        Func<dynamic, object> converter)
+        : ISpecimenBuilder
+    {
+        public object Create(object request, ISpecimenContext context)
+        {
+            if (GetRequestType(request) is { } type
+                && type.IsGenericType
+                && type.GetGenericTypeDefinition() == immutableType
+                && type.GetGenericArguments() is { Length: > 0 } args)
+            {
+                var listType = underlyingType.MakeGenericType(args);
+                dynamic list = context.Resolve(listType);
+
+                return converter.Invoke(list);
+            }
+
+            return new NoSpecimen();
+        }
+
+        private static Type? GetRequestType(object request)
+            => request switch
+            {
+                ParameterInfo pi => pi.ParameterType,
+                Type t => t,
+                _ => null,
+            };
+    }
+}
+#endif