From c345ce6647861c327028ce2c9a191ce425c8f7fa Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jos=C3=A9=20Sim=C3=B5es?= <jose.simoes@eclo.solutions>
Date: Thu, 23 Jul 2026 10:36:36 +0100
Subject: [PATCH 1/2] Add new generic collections unit tests

---
 Tests/GenericCollections/ListTests.cs | 34 +++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/Tests/GenericCollections/ListTests.cs b/Tests/GenericCollections/ListTests.cs
index a217572..d611d46 100644
--- a/Tests/GenericCollections/ListTests.cs
+++ b/Tests/GenericCollections/ListTests.cs
@@ -1203,6 +1203,32 @@ public void List_GenericMethod_NewObj_InsertAndIterate()
             Assert.AreEqual(4, result[3]);
         }
 
+        [TestMethod]
+        public void List_StaticField_ValueType_Add()
+        {
+            // Reproduces nanoframework/Home#1821: a List<T> held in a static readonly
+            // field initialized via a field initializer (i.e. constructed from the
+            // declaring type's own .cctor), then Add()'d to from another method.
+            StaticListHolder.Numbers.Add(1);
+            StaticListHolder.Numbers.Add(2);
+
+            Assert.AreEqual(2, StaticListHolder.Numbers.Count);
+            Assert.AreEqual(1, StaticListHolder.Numbers[0]);
+            Assert.AreEqual(2, StaticListHolder.Numbers[1]);
+        }
+
+        [TestMethod]
+        public void List_StaticField_ReferenceType_Add()
+        {
+            // Reproduces nanoframework/Home#1821 with a reference-type element,
+            // mirroring the reported List<Ds18b20> Sensors static field.
+            StaticListHolder.Items.Add(new DummyClass(1, "One"));
+
+            Assert.AreEqual(1, StaticListHolder.Items.Count);
+            Assert.AreEqual(1, StaticListHolder.Items[0].Id);
+            Assert.AreEqual("One", StaticListHolder.Items[0].Name);
+        }
+
         // Generic helper methods that exercise NEWOBJ with MVAR TypeSpecs.
         // Each method creates a new List<T> from within a generic method body,
         // producing IL with MethodRef tokens whose owner TypeSpec is List<!!0>.
@@ -1316,6 +1342,14 @@ public DummyClass(int id, string name)
         }
     }
 
+    // Field initializers below run as part of this type's own .cctor, matching the
+    // pattern reported in nanoframework/Home#1821 (`private static readonly List<T> ... = new List<T>();`).
+    internal static class StaticListHolder
+    {
+        internal static readonly List<int> Numbers = new List<int>();
+        internal static readonly List<DummyClass> Items = new List<DummyClass>();
+    }
+
     internal struct DummyStruct
     {
         public int Id { get; set; }

From a4601027b43daded599faf604af0f3ed46d90a95 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Jos=C3=A9=20Sim=C3=B5es?= <jose.simoes@eclo.solutions>
Date: Thu, 23 Jul 2026 11:03:47 +0100
Subject: [PATCH 2/2] Fixes from code review

---
 Tests/GenericCollections/ListTests.cs | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/Tests/GenericCollections/ListTests.cs b/Tests/GenericCollections/ListTests.cs
index d611d46..7dd1061 100644
--- a/Tests/GenericCollections/ListTests.cs
+++ b/Tests/GenericCollections/ListTests.cs
@@ -11,6 +11,16 @@ namespace GenericCollections
     [TestClass]
     public class ListTests
     {
+        [Cleanup]
+        public void CleanupTests()
+        {
+            // StaticListHolder is shared static state (see nanoframework/Home#1821
+            // repro below); clear it so List_StaticField_* tests start empty on
+            // every run/retry, even if a prior test's assertions failed.
+            StaticListHolder.Numbers.Clear();
+            StaticListHolder.Items.Clear();
+        }
+
         [TestMethod]
         public void List_Constructor_Default()
         {