Add args-test to Integer#to_d

vm/integer.go

@@ -393,6 +393,10 @@ func builtinIntegerInstanceMethods() []*BuiltinMethodObject {
 			Name: "to_d",
 			Fn: func(receiver Object, sourceLine int) builtinMethodBody {
 				return func(t *thread, args []Object, blockFrame *normalCallFrame) Object {
+					if len(args) > 1 {
+						return t.vm.initErrorObject(errors.ArgumentError, sourceLine, "Expect 0 or 1 argument. got: %d", len(args))
+					}
+					// TODO: implement the digit truncation in other PR
 					r := receiver.(*IntegerObject)
 					return t.vm.initDecimalObject(intToDecimal(r))
 				}

vm/integer_test.go

@@ -245,6 +245,20 @@ func TestIntegerConversion(t *testing.T) {
 	}
 }
 
+func TestIntegerConversonFail(t *testing.T) {
+	testsFail := []errorTestCase{
+		{`100.to_d(1, 2, 3)`, "ArgumentError: Expect 0 or 1 argument. got: 3", 1},
+	}
+
+	for i, tt := range testsFail {
+		v := initTestVM()
+		evaluated := v.testEval(t, tt.input, getFilename())
+		checkErrorMsg(t, i, evaluated, tt.expected)
+		v.checkCFP(t, i, tt.expectedCFP)
+		v.checkSP(t, i, 1)
+	}
+}
+
 // Method test
 
 func TestIntegerEvenMethod(t *testing.T) {