Fix cast to nil when nil is expected

Resolves `TypeCastError: The return type of stub #... : Nil at ...:##
doesn't match the expected type Nil`

src/spectator/mocks/double.cr

@@ -38,7 +38,7 @@ module Spectator::Mocks
         %call = ::Spectator::Mocks::GenericMethodCall.new({{name.symbolize}}, %args)
         ::Spectator::Mocks::Registry.record_call(self, %call)
         if (%stub = ::Spectator::Mocks::Registry.find_stub(self, %call))
-          %stub.call(%args, typeof(%method({{args.splat}})))
+          %stub.call!(%args, typeof(%method({{args.splat}})))
         else
           %method({{args.splat}})
         end
@@ -49,7 +49,7 @@ module Spectator::Mocks
         %call = ::Spectator::Mocks::GenericMethodCall.new({{name.symbolize}}, %args)
         ::Spectator::Mocks::Registry.record_call(self, %call)
         if (%stub = ::Spectator::Mocks::Registry.find_stub(self, %call))
-          %stub.call(%args, typeof(%method({{args.splat}}) { |*%ya| yield *%ya }))
+          %stub.call!(%args, typeof(%method({{args.splat}}) { |*%ya| yield *%ya }))
         else
           %method({{args.splat}}) do |*%yield_args|
             yield *%yield_args

src/spectator/mocks/method_stub.cr

@@ -12,6 +12,15 @@ module Spectator::Mocks
 
     abstract def call(args : GenericArguments(T, NT), rt : RT.class) forall T, NT, RT
 
+    def call!(args : GenericArguments(T, NT), rt : RT.class) : RT forall T, NT, RT
+      value = call(args, rt)
+      if value.is_a?(RT)
+        value.as(RT)
+      else
+        raise TypeCastError.new("The return type of stub #{self} doesn't match the expected type #{RT}")
+      end
+    end
+
     def to_s(io)
       io << '#'
       io << @name

src/spectator/mocks/nil_method_stub.cr

@@ -4,12 +4,8 @@ require "./value_method_stub"
 
 module Spectator::Mocks
   class NilMethodStub < GenericMethodStub(Nil)
-    def call(_args : GenericArguments(T, NT), rt : RT.class) forall T, NT, RT
+    def call(_args : GenericArguments(T, NT), _rt : RT.class) forall T, NT, RT
-      if (cast = nil.as?(RT))
+      nil
-        cast
-      else
-        raise "The return type of stub #{self} doesn't match the expected type #{RT}"
-      end
     end
 
     def and_return(value : T) forall T

src/spectator/mocks/proc_method_stub.cr

@@ -8,12 +8,7 @@ module Spectator::Mocks
     end
 
     def call(_args : GenericArguments(T, NT), rt : RT.class) forall T, NT, RT
-      result = @proc.call
+      @proc.call
-      if (cast = result.as?(RT))
-        cast
-      else
-        raise "The return type of stub #{self} doesn't match the expected type #{RT}"
-      end
     end
   end
 end

src/spectator/mocks/stubs.cr

@@ -38,7 +38,7 @@ module Spectator::Mocks
         %call = ::Spectator::Mocks::GenericMethodCall.new({{name.symbolize}}, %args)
         ::Spectator::Mocks::Registry.record_call(self, %call)
         if (%stub = ::Spectator::Mocks::Registry.find_stub(self, %call))
-          %stub.call(%args, typeof({{original}}({{args.splat}})))
+          %stub.call!(%args, typeof({{original}}({{args.splat}})))
         else
           {{original}}({{args.splat}})
         end
@@ -49,7 +49,7 @@ module Spectator::Mocks
         %call = ::Spectator::Mocks::GenericMethodCall.new({{name.symbolize}}, %args)
         ::Spectator::Mocks::Registry.record_call(self, %call)
         if (%stub = ::Spectator::Mocks::Registry.find_stub(self, %call))
-          %stub.call(%args, typeof({{original}}({{args.splat}}) { |*%ya| yield *%ya }))
+          %stub.call!(%args, typeof({{original}}({{args.splat}}) { |*%ya| yield *%ya }))
         else
           {{original}}({{args.splat}}) do |*%yield_args|
             yield *%yield_args

src/spectator/mocks/value_method_stub.cr

@@ -8,12 +8,7 @@ module Spectator::Mocks
     end
 
     def call(_args : GenericArguments(T, NT), rt : RT.class) forall T, NT, RT
-      result = @value
+      @value
-      if (cast = result.as?(RT))
-        cast
-      else
-        raise "The return type of stub #{self} doesn't match the expected type #{RT}"
-      end
     end
   end
 end