test: Db tests assert stored state instead of smoke-calling empty methods

src/Nethermind/Nethermind.Db.Test/DbOnTheRocksTests.cs

@@ -564,7 +564,7 @@ public void Smoke_test_span_with_memory_manager()
         };
 
         [Test]
-        public void Can_get_all_on_empty() => _ = _db.GetAll().ToList();
+        public void Can_get_all_on_empty() => Assert.That(_db.GetAll(), Is.Empty);
 
         [Test]
         public void Smoke_test_iterator()

src/Nethermind/Nethermind.Db.Test/MemDbTests.cs

@@ -31,8 +31,13 @@ public void Can_create_with_delays()
         {
             MemDb memDb = new(10, 10);
             memDb.Set(TestItem.KeccakA, new byte[] { 1, 2, 3 });
-            memDb.Get(TestItem.KeccakA);
-            _ = memDb[new[] { TestItem.KeccakA.BytesToArray() }];
+            byte[]? direct = memDb.Get(TestItem.KeccakA);
+            KeyValuePair<byte[], byte[]>[] batch = memDb[new[] { TestItem.KeccakA.BytesToArray() }];
+            using (Assert.EnterMultipleScope())
+            {
+                Assert.That(direct, Is.EqualTo(new byte[] { 1, 2, 3 }));
+                Assert.That(batch[0].Value, Is.EqualTo(new byte[] { 1, 2, 3 }));
+            }
         }
 
         [Test]
@@ -49,7 +54,7 @@ public void Can_create_without_arguments()
         {
             MemDb memDb = new();
             memDb.Set(TestItem.KeccakA, new byte[] { 1, 2, 3 });
-            memDb.Get(TestItem.KeccakA);
+            Assert.That(memDb.Get(TestItem.KeccakA), Is.EqualTo(new byte[] { 1, 2, 3 }));
         }
 
         [Test]
@@ -133,20 +138,6 @@ public void Can_get_values()
             Assert.That(memDb.Values, Has.Count.EqualTo(2));
         }
 
-        [Test]
-        public void Dispose_does_not_cause_trouble()
-        {
-            MemDb memDb = new();
-            memDb.Dispose();
-        }
-
-        [Test]
-        public void Flush_does_not_cause_trouble()
-        {
-            MemDb memDb = new();
-            memDb.Flush();
-        }
-
         [Test]
         public void Can_get_all_ordered()
         {

src/Nethermind/Nethermind.Db.Test/ReadOnlyDbProviderTests.cs

@@ -1,6 +1,9 @@
 // SPDX-FileCopyrightText: 2022 Demerzel Solutions Limited
 // SPDX-License-Identifier: LGPL-3.0-only
 
+using System;
+using Nethermind.Core;
+using Nethermind.Core.Test.Builders;
 using NSubstitute;
 using NUnit.Framework;
 
@@ -13,8 +16,35 @@ public class ReadOnlyDbProviderTests
         [TestCase(false)]
         public void Can_clear(bool localChanges)
         {
-            ReadOnlyDbProvider dbProvider = new(Substitute.For<IDbProvider>(), localChanges);
+            MemDb wrappedDb = new();
+            wrappedDb.Set(TestItem.KeccakA, [1, 2, 3]);
+            IDbProvider wrappedProvider = Substitute.For<IDbProvider>();
+            wrappedProvider.GetDb<IDb>("test").Returns(wrappedDb);
+
+            ReadOnlyDbProvider dbProvider = new(wrappedProvider, localChanges);
+            IDb readOnlyDb = dbProvider.GetDb<IDb>("test");
+
+            if (localChanges)
+            {
+                readOnlyDb.Set(TestItem.KeccakB, [4, 5, 6]);
+                Assert.That(readOnlyDb.Get(TestItem.KeccakB), Is.EqualTo(new byte[] { 4, 5, 6 }));
+            }
+            else
+            {
+                Assert.Throws<InvalidOperationException>(() => readOnlyDb.Set(TestItem.KeccakB, [4, 5, 6]));
+            }
+
             dbProvider.ClearTempChanges();
+
+            using (Assert.EnterMultipleScope())
+            {
+                if (localChanges)
+                {
+                    Assert.That(readOnlyDb.Get(TestItem.KeccakB), Is.Null, "the in-memory overlay must be dropped");
+                }
+
+                Assert.That(readOnlyDb.Get(TestItem.KeccakA), Is.EqualTo(new byte[] { 1, 2, 3 }), "the wrapped db must be untouched");
+            }
         }
     }
 }

src/Nethermind/Nethermind.Db.Test/SnapshotableMemColumnsDbTests.cs

@@ -156,20 +156,6 @@ public void Can_use_write_batch()
             Assert.That(column1.Get(TestItem.KeccakA), Is.EqualTo(_sampleValue));
         }
 
-        [Test]
-        public void Flush_does_not_cause_trouble()
-        {
-            SnapshotableMemColumnsDb<TestColumns> columnsDb = new();
-            columnsDb.Flush();
-        }
-
-        [Test]
-        public void Dispose_does_not_cause_trouble()
-        {
-            SnapshotableMemColumnsDb<TestColumns> columnsDb = new();
-            columnsDb.Dispose();
-        }
-
         [Test]
         public void ColumnKeys_returns_all_columns()
         {

src/Nethermind/Nethermind.Db.Test/SnapshotableMemDbTests.cs

@@ -190,20 +190,6 @@ public void Can_get_values()
             Assert.That(memDb.Values, Has.Count.EqualTo(2));
         }
 
-        [Test]
-        public void Dispose_does_not_cause_trouble()
-        {
-            SnapshotableMemDb memDb = new();
-            memDb.Dispose();
-        }
-
-        [Test]
-        public void Flush_does_not_cause_trouble()
-        {
-            SnapshotableMemDb memDb = new();
-            memDb.Flush();
-        }
-
         [Test]
         public void Can_clear()
         {