public void MathExpressionContext_Can_Redefine_Variable()
{
MathExpressionContext context = new MathExpressionContext();
context.Define("x", 42);
Assert.AreEqual(42, context.Resolve("x").Evaluate(context));
context.Define("x", 107);
Assert.AreEqual(107, context.Resolve("x").Evaluate(context));
}