private void TestThatOperatorYields(Operator op, string input, string expectedResult)
        {
            var operand = new StringLiteral(input);
            var expr    = new OperatorExpression(op, operand);

            expr.TryEvaluate(EmptyEnvironment, out string actualResult).Should().BeTrue();
            actualResult.Should().Be(expectedResult);
        }
        public void TestThatEvalFailsIfInnerExpressionCannotBeEvaluated()
        {
            var concat = new OperatorExpression(AnyValidOperator, AnyUnevaluatableExpr);

            concat.TryEvaluate(EmptyEnvironment, out string value).Should().BeFalse();
        }