public void fct_OP_a_CP_retDouble_P1String_ok()
{
ExpressionEval evaluator = new ExpressionEval();
// definir langue: fr ou en, sert pour les opérateurs: ET/AND, OU/OR, NON/NOT.
evaluator.SetLang(Language.En);
string expr = "fct(a)";
ParseResult parseResult = evaluator.Parse(expr);
//====2/prepare the execution, provide all used variables: type and value
//ExprExecResult execResult = evaluator.InitExec();
// 3 letters -> return 3x1.5=4.5
evaluator.DefineVarString("a", "abc");
// link function body to function call
evaluator.AttachFunction("Fct", FctDouble_String);
//====3/execute l'expression booléenne
ExecResult execResult = evaluator.Exec();
Assert.AreEqual(false, execResult.HasError, "The exec of the expression should finish with success");
// check the final result value (is ExprExecFunctionCallBool override ExprExecValueBool)
ExprExecValueDouble valueDouble = execResult.ExprExec as ExprExecValueDouble;
Assert.IsNotNull(valueDouble, "The result value should be a double");
Assert.AreEqual(4.5, valueDouble.Value, "The result value should be: true");
}