Smarter handling of stub fallback

spec/spectator/mocks/null_double_spec.cr

@@ -34,6 +34,30 @@ Spectator.describe Spectator::NullDouble do
     end
   end
 
+  context "with abstract stubs and return type annotations" do
+    Spectator::NullDouble.define(TestDouble) do
+      abstract_stub abstract def foo(value) : String
+    end
+
+    let(arguments) { Spectator::Arguments.capture(/foo/) }
+    let(stub) { Spectator::ValueStub.new(:foo, "bar", arguments).as(Spectator::Stub) }
+    subject(dbl) { TestDouble.new([stub]) }
+
+    it "enforces the return type" do
+      expect(dbl.foo("foobar")).to compile_as(String)
+    end
+
+    it "raises on non-matching arguments" do
+      expect { dbl.foo("bar") }.to raise_error(TypeCastError, /String/)
+    end
+
+    it "raises on non-matching stub" do
+      stub = Spectator::ValueStub.new(:foo, 42, arguments).as(Spectator::Stub)
+      dbl._spectator_define_stub(stub)
+      expect { dbl.foo("foobar") }.to raise_error(TypeCastError, /String/)
+    end
+  end
+
   context "with common object methods" do
     subject(dbl) do
       EmptyDouble.new([
@@ -102,6 +126,7 @@ Spectator.describe Spectator::NullDouble do
       io = IO::Memory.new
       pp = PrettyPrint.new(io)
       aggregate_failures do
+        # Methods that would cause type cast errors are omitted from this list.
         expect_null_double(dbl, dbl.!=(42))
         expect_null_double(dbl, dbl.!~(42))
         expect_null_double(dbl, dbl.==(42))
@@ -111,21 +136,10 @@ Spectator.describe Spectator::NullDouble do
         expect_null_double(dbl, dbl.dup)
         expect_null_double(dbl, dbl.hash(42))
         expect_null_double(dbl, dbl.hash)
-        # expect(dbl.in?(42)).to be(dbl)
-        # expect(dbl.in?(1, 2, 3)).to be(dbl)
-        expect_null_double(dbl, dbl.inspect)
         expect_null_double(dbl, dbl.itself)
         expect_null_double(dbl, dbl.not_nil!)
-        expect_null_double(dbl, dbl.pretty_inspect)
         expect_null_double(dbl, dbl.tap { nil })
-        expect_null_double(dbl, dbl.to_json)
-        expect_null_double(dbl, dbl.to_pretty_json)
-        expect_null_double(dbl, dbl.to_s)
-        expect_null_double(dbl, dbl.to_yaml)
         expect_null_double(dbl, dbl.try { nil })
-        # expect(dbl.object_id).to be(dbl)
-        # expect(dbl.same?(dbl)).to be(dbl)
-        # expect(dbl.same?(nil)).to be(dbl)
       end
     end
   end
@@ -135,7 +149,7 @@ Spectator.describe Spectator::NullDouble do
 
     context "without common object methods" do
       Spectator::NullDouble.define(TestDouble) do
-        abstract_stub abstract def foo(value) : String
+        abstract_stub abstract def foo(value)
       end
 
       let(stub) { Spectator::ValueStub.new(:foo, "bar", arguments).as(Spectator::Stub) }
@@ -152,10 +166,6 @@ Spectator.describe Spectator::NullDouble do
       it "returns self when argument count doesn't match" do
         expect_null_double(dbl, dbl.foo)
       end
-
-      it "has a union return type with self" do
-        expect(dbl.foo("foobar")).to compile_as(String | TestDouble)
-      end
     end
 
     context "with common object methods" do
@@ -167,7 +177,7 @@ Spectator.describe Spectator::NullDouble do
       subject(dbl) { TestDouble.new([stub]) }
 
       it "returns the response when constraint satisfied" do
-        expect(dbl.hash("foobar")).to eq(true)
+        expect(dbl.hash("foobar")).to eq(12345)
       end
 
       it "returns self when constraint unsatisfied" do
@@ -177,10 +187,6 @@ Spectator.describe Spectator::NullDouble do
       it "returns self when argument count doesn't match" do
         expect_null_double(dbl, dbl.hash)
       end
-
-      it "has a union return type with self" do
-        expect(dbl.hash("foobar")).to compile_as(Int32 | TestDouble)
-      end
     end
   end
 

src/spectator/mocks/double.cr

@@ -81,6 +81,22 @@ module Spectator
       {% end %}
     end
 
+    private def _spectator_stub_fallback(call : MethodCall, &)
+      yield
+    end
+
+    private def _spectator_stub_fallback(call : MethodCall, type, &)
+      yield
+    end
+
+    private def _spectator_abstract_stub_fallback(call : MethodCall)
+      raise UnexpectedMessage.new("#{_spectator_stubbed_name} received unexpected message #{call}")
+    end
+
+    private def _spectator_abstract_stub_fallback(call : MethodCall, type)
+      raise UnexpectedMessage.new("#{_spectator_stubbed_name} received unexpected message #{call}")
+    end
+
     # "Hide" existing methods and methods from ancestors by overriding them.
     macro finished
       stub_all {{@type.name(generic_args: false)}}

src/spectator/mocks/null_double.cr

@@ -81,6 +81,30 @@ module Spectator
       {% end %}
     end
 
+    private def _spectator_stub_fallback(call : MethodCall, &)
+      self
+    end
+
+    private def _spectator_stub_fallback(call : MethodCall, type : self, &)
+      self
+    end
+
+    private def _spectator_stub_fallback(call : MethodCall, type, &)
+      yield
+    end
+
+    private def _spectator_abstract_stub_fallback(call : MethodCall)
+      self
+    end
+
+    private def _spectator_abstract_stub_fallback(call : MethodCall, type : self)
+      self
+    end
+
+    private def _spectator_abstract_stub_fallback(call : MethodCall, type)
+      raise TypeCastError.new("#{_spectator_stubbed_name} received message #{call} and is attempting to return `self`, but returned type must be `#{type}`.")
+    end
+
     # "Hide" existing methods and methods from ancestors by overriding them.
     macro finished
       stub_all {{@type.name(generic_args: false)}}

src/spectator/mocks/stubbable.cr

@@ -19,6 +19,42 @@ module Spectator
     # Utility returning the mock or double's name as a string.
     abstract def _spectator_stubbed_name : String
 
+    # Method called when a stub isn't found.
+    #
+    # The received message is captured in *call*.
+    # Yield to call the original method's implementation.
+    # The stubbed method returns the value returned by this method.
+    # This method can also raise an error if it's impossible to return something.
+    abstract def _spectator_stub_fallback(call : MethodCall, &)
+
+    # Method called when a stub isn't found.
+    #
+    # The received message is captured in *call*.
+    # The expected return type is provided by *type*.
+    # Yield to call the original method's implementation.
+    # The stubbed method returns the value returned by this method.
+    # This method can also raise an error if it's impossible to return something.
+    abstract def _spectator_stub_fallback(call : MethodCall, type, &)
+
+    # Method called when a stub isn't found.
+    #
+    # This is similar to `#_spectator_stub_fallback`,
+    # but called when the original (un-stubbed) method isn't available.
+    # The received message is captured in *call*.
+    # The stubbed method returns the value returned by this method.
+    # This method can also raise an error if it's impossible to return something.
+    abstract def _spectator_abstract_stub_fallback(call : MethodCall)
+
+    # Method called when a stub isn't found.
+    #
+    # This is similar to `#_spectator_stub_fallback`,
+    # but called when the original (un-stubbed) method isn't available.
+    # The received message is captured in *call*.
+    # The expected return type is provided by *type*.
+    # The stubbed method returns the value returned by this method.
+    # This method can also raise an error if it's impossible to return something.
+    abstract def _spectator_abstract_stub_fallback(call : MethodCall, type)
+
     # Redefines a method to accept stubs.
     #
     # The *method* should be a `Def`.
@@ -78,11 +114,12 @@ module Spectator
             %stub.value
           {% end %}
         else
-          {% if method.abstract? %}
-            # Response not configured for this method/message.
-            raise ::Spectator::UnexpectedMessage.new("#{_spectator_stubbed_name} received unexpected message :{{method.name}} with #{%args}")
+          {% if !method.abstract? %}
+            _spectator_stub_fallback(%call, typeof({{original}})) { {{original}} }
+          {% elsif method.return_type %}
+            _spectator_abstract_stub_fallback(%call, {{method.return_type}})
           {% else %}
-            {{original}}
+            _spectator_abstract_stub_fallback(%call)
           {% end %}
         end
       end
@@ -138,8 +175,11 @@ module Spectator
             %stub.value
           {% end %}
         else
-          # Response not configured for this method/message.
-          raise ::Spectator::UnexpectedMessage.new("#{_spectator_stubbed_name} received unexpected message :{{method.name}} with #{%args}")
+          {% if method.return_type %}
+            _spectator_abstract_stub_fallback(%call, {{method.return_type}})
+          {% else %}
+            _spectator_abstract_stub_fallback(%call)
+          {% end %}
         end
       end
     end