Possibility to override type if construction fails.

Author: Robert Lindblom

AutoMockerNSubstitute.1.0.1.nupkg

@@ -73,6 +73,12 @@ public void ThrowsExceptionIfNoMatchAvailable()
             Assert.Throws<ConstructorMatchException>(() => new NSubstituteAutoMocker<ClassWithAllConstructors>([typeof(IDependency2), typeof(IDependency1)]));
         }
 
+        [Fact]
+        public void ThrowsExceptionIfNotSubstitutableParam()
+        {
+            Assert.Throws<ArgumentException>(() => new NSubstituteAutoMocker<ClassWithNotSubstitutableConstructorParam>());
+        }
+
         [Fact]
         public void CanOverrideParameterViaEvent()
         {
@@ -101,6 +107,19 @@ public void CanOverrideParameterViaEventAlt()
 
             Assert.IsAssignableFrom<Dependency1VitoImplementation>(autoMocker.ClassUnderTest.Dependency1);
         }
+
+        [Fact]
+        public void ThrowsExceptionIfOverrideIsNull()
+        {
+            Assert.Throws<ArgumentException>(() => new NSubstituteAutoMocker<ClassWithNotSubstitutableConstructorParam>((_, _) => null));
+        }
+
+        [Fact]
+        public void CanOverrideNotSubstitutableParam()
+        {
+            new NSubstituteAutoMocker<ClassWithNotSubstitutableConstructorParam>((paramInfo, obj) =>
+                paramInfo.ParameterType == typeof(ConcreteClass) ? new ConcreteClassForTest() : obj);
+        }
     }
 
     public class Get

source/NSubstituteAutoMocker.UnitTests/AutoMockerNSubstitute.cs

@@ -0,0 +1,3 @@
+namespace AutoMockerNSubstitute.UnitTests.SamplesToTest;
+
+public class ClassWithNotSubstitutableConstructorParam(ConcreteClass testClass);

source/NSubstituteAutoMocker.UnitTests/SamplesToTest/ClassWithNotSubstitutableConstructorParam.cs

@@ -0,0 +1,4 @@
+namespace AutoMockerNSubstitute.UnitTests.SamplesToTest;
+
+public class ConcreteClass(int param);
+public class ConcreteClassForTest() : ConcreteClass(0);

source/NSubstituteAutoMocker.UnitTests/SamplesToTest/ConcreteClass.cs

@@ -35,11 +35,28 @@ public NSubstituteAutoMocker(Type[] parameterTypes, Func<ParameterInfo, object,
         foreach (ParameterInfo info in parameters)
         {
             Type type = info.ParameterType;
-            var constructorArg = CreateInstance(type);
+            object constructorArg = null;
+            ArgumentException exception = null;
+
+            try
+            {
+                constructorArg = CreateInstance(type);
+            }
+            catch (ArgumentException e)
+            {
+                // Give caller a chance to override the parameter.
+                exception = e;
+            }
+            
             if (parameterOverrideFunc != null)
             {
                 constructorArg = parameterOverrideFunc(info, constructorArg);
             }
+
+            if (constructorArg == null && exception != null)
+            {
+                throw exception;
+            }
             _constructors.Add(info, constructorArg);
         }