Provide unit test for RegisterMapping issue (#419)

When using RegisterMapping to register a covariant interface type, resolving it
may fail.

Issue #418

test/DryIoc.IssuesTests/GHIssue418_ResolveCovariantBaseType.cs

@@ -0,0 +1,92 @@
+using NUnit.Framework;
+using System.Collections.Generic;
+
+namespace DryIoc.IssuesTests
+{
+    [TestFixture]
+    public class GHIssue418_ResolveCovariantBaseType
+    {
+        /// <summary>
+        ///     Currently, resolving the list as <see cref="IReadOnlyList{BaseClass}" /> fails in this test.
+        ///     The list is registered as its implementation and mapped to the interface.
+        /// </summary>
+        [Test, Ignore("fixme")]
+        public void RegisterCovariantImplementationTypeWithMapping()
+        {
+            var container = new Container();
+            // Register the implementation as itself
+            container.Register(Made.Of(() => new List<SubClass>()));
+            // Register the interface with base type parameter
+            container.RegisterMapping<IReadOnlyList<BaseClass>, List<SubClass>>();
+
+            // Resolving IReadOnlyList<BaseClass> crashes here
+            var baseClassList = container.Resolve<IReadOnlyList<BaseClass>>();
+            Assert.IsInstanceOf<List<SubClass>>(baseClassList);
+        }
+
+        /// <summary>
+        ///     This works. The difference is that the list is registered as <see cref="IReadOnlyList{SubClass}"/> and
+        ///     then it is mapped.
+        /// </summary>
+        [Test]
+        public void RegisterCovariantInterfaceTypeWithMapping()
+        {
+            var container = new Container();
+            container.Register(Made.Of<IReadOnlyList<SubClass>>(() => new List<SubClass>()));
+            container.RegisterMapping<IReadOnlyList<BaseClass>, IReadOnlyList<SubClass>>();
+
+            var baseClassList = container.Resolve<IReadOnlyList<BaseClass>>();
+            Assert.IsInstanceOf<List<SubClass>>(baseClassList);
+        }
+
+        /// <summary>
+        ///     This also works, because there is no mapping here.
+        /// </summary>
+        [Test]
+        public void RegisterCovariantListTypeDirect()
+        {
+            var container = new Container();
+            container.Register<IReadOnlyList<BaseClass>, List<SubClass>>(Made.Of(() => new List<SubClass>()));
+
+            var baseClassList = container.Resolve<IReadOnlyList<BaseClass>>();
+            Assert.IsInstanceOf<List<SubClass>>(baseClassList);
+        }
+
+        /// <summary>
+        ///     This works, but the registration code is weird, because we assign a closed generic implementation to an open
+        ///     generic service.
+        /// </summary>
+        [Test]
+        public void RegisterClosedGenericImplementationAsOpenGeneric()
+        {
+            var container = new Container();
+            container.Register(typeof(IReadOnlyList<>), typeof(List<SubClass>),
+                               made: Made.Of(FactoryMethod.ConstructorWithResolvableArguments));
+
+            var baseClassList = container.Resolve<IReadOnlyList<BaseClass>>();
+            Assert.IsInstanceOf<List<SubClass>>(baseClassList);
+        }
+
+        /// <summary>
+        ///     This is a workaround by using a delegate instead of a mapping.
+        /// </summary>
+        [Test]
+        public void RegisterCovariantImplementationTypeWithDelegete()
+        {
+            var container = new Container();
+            container.Register(Made.Of(() => new List<SubClass>()));
+            container.RegisterDelegate<IReadOnlyList<BaseClass>>(c => c.Resolve<List<SubClass>>());
+
+            var baseClassList = container.Resolve<IReadOnlyList<BaseClass>>();
+            Assert.IsInstanceOf<List<SubClass>>(baseClassList);
+        }
+
+        private class BaseClass
+        {
+        }
+
+        private class SubClass : BaseClass
+        {
+        }
+    }
+}