Restore MethodCollector tests

src/MagicOnion.Client.SourceGenerator/CodeAnalysis/MethodCollector.cs

@@ -8,7 +8,7 @@ namespace MagicOnion.Client.SourceGenerator.CodeAnalysis;
 /// <summary>
 /// Provides logic to collect MagicOnion Services and StreamingHubs from a compilation.
 /// </summary>
-public class MethodCollector
+public static class MethodCollector
 {
     public static (MagicOnionServiceCollection ServiceCollection, IReadOnlyList<Diagnostic> Diagnostics) Collect(ImmutableArray<INamedTypeSymbol> interfaceSymbols, ReferenceSymbols referenceSymbols, CancellationToken cancellationToken)
     {

tests/MagicOnion.Client.SourceGenerator.Tests/Collector/MethodCollectorHelper.cs

@@ -0,0 +1,24 @@
+using Microsoft.CodeAnalysis;
+
+namespace MagicOnion.Client.SourceGenerator.Tests.Collector;
+
+public static class MethodCollectorTestHelper
+{
+    public static IEnumerable<INamedTypeSymbol> Traverse(INamespaceOrTypeSymbol rootNamespaceOrTypeSymbol)
+    {
+        foreach (var namespaceOrTypeSymbol in rootNamespaceOrTypeSymbol.GetMembers())
+        {
+            if (namespaceOrTypeSymbol is INamedTypeSymbol { TypeKind: TypeKind.Interface } typeSymbol)
+            {
+                yield return typeSymbol;
+            }
+            else if (namespaceOrTypeSymbol is INamespaceSymbol namespaceSymbol)
+            {
+                foreach (var t in Traverse(namespaceSymbol))
+                {
+                    yield return t;
+                }
+            }
+        }
+    }
+}