InterpreterImpl

InterpreterImpl.cs

using System;

namespace Interpreter {
    public abstract class AbstractInterpreter {
        public abstract int Interpret (Context context);
    }
}

namespace Interpreter {
    public class Context {
        public TerminalExpression[] TerminalExpressionArgs { get; set; }

        public readonly int MULTIPLIER = 2;
    }
}

namespace Interpreter {
    public class NonTerminalExpression : AbstractInterpreter {
        public Func<int, int, int> BinaryOperation { get; set; } = (a, b) => 0;
        public override int Interpret (Context context) {
            if (context.TerminalExpressionArgs.Length < 2) {
                throw new ArgumentException ("should be at least 2 terminal params");
            }
            return BinaryOperation?.Invoke (context.TerminalExpressionArgs[0].Interpret (context), context.TerminalExpressionArgs[1].Interpret (context)) ?? 0;
        }
    }
}

namespace Interpreter {
    public class TerminalExpression : AbstractInterpreter {
        public int Value { get; set; } = 1;
        public TerminalExpression (int value) {
            Value = value;
        }

        public override int Interpret (Context context) {
            //although probably interpreter should not contain actual state to interpret
            return context.MULTIPLIER * Value;
        }
    }
}

Program.cs

using System;
using System.Collections.Generic;
using Interpreter;

public class Program
{
    public static void Main()
    {
            var context = new Context();
            context.TerminalExpressionArgs = new TerminalExpression[] {
                new TerminalExpression(1),
                new TerminalExpression(2)
            };

            AbstractInterpreter[] interpreters = new AbstractInterpreter[]{
                new TerminalExpression(3),
                new NonTerminalExpression(){BinaryOperation = (a, b)=>a*b}
            };
            Assert.Equal(6, interpreters[0].Interpret(context));
            Assert.Equal(8, interpreters[1].Interpret(context));

        TestRunner.Print();
    }
}

XUnit.Utils.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.CompilerServices;

public static class Assert {
    public static void Equal<T> (T a, T b, [CallerMemberName] string callerName = "", [CallerLineNumber] int callerLine = 0) {
        if (!a.Equals (b)) {
            // throw new Exception ($"{a} doesn't equal to {b}");
            TestRunner.AddResult (
                new TestRunResult () {
                    CallerName = callerName,
                        CallerLine = callerLine.ToString (),
                        Success = false,
                        Assertion = "Equal<T>",
                        ErrorMessage = $"{a} doesn't equal to {b}"
                });
        } else {
            TestRunner.AddResult (
                new TestRunResult () {
                    CallerName = callerName,
                        CallerLine = callerLine.ToString (),
                        Success = true,
                        Assertion = "Single<T>"
                });
        }
    }

    public static void Equal<T> (IEnumerable<T> a,
        IEnumerable<T> b, [CallerMemberName] string callerName = "", [CallerLineNumber] int callerLine = 0) {
        if (a.Count () != b.Count ()) {
            TestRunner.AddResult (
                new TestRunResult () {
                    CallerName = callerName,
                        CallerLine = callerLine.ToString (),
                        Success = false,
                        Assertion = "Equal<T>",
                        ErrorMessage = $"a.{a.Count()} != b.{b.Count()}"
                });
        } else if (!a.SequenceEqual (b)) {
            TestRunner.AddResult (
                new TestRunResult () {
                    CallerName = callerName,
                        CallerLine = callerLine.ToString (),
                        Success = false,
                        Assertion = "SequenceEqual<T>",
                        ErrorMessage = $"Different sequences"
                });
        } else {
            TestRunner.AddResult (
                new TestRunResult () {
                    CallerName = callerName,
                        CallerLine = callerLine.ToString (),
                        Success = true,
                        Assertion = "Equal<T>"
                });
        }
    }

    public static void Single<T> (IEnumerable<T> collection, [CallerMemberName] string callerName = "", [CallerLineNumber] int callerLine = 0) {
        if (collection.Count () != 1) {
            // throw new Exception ("Collection doesn't contain 1 element");
            TestRunner.AddResult (
                new TestRunResult () {
                    CallerName = callerName,
                        CallerLine = callerLine.ToString (),
                        Success = false,
                        Assertion = "Single<T>",
                        ErrorMessage = "Collection doesn't contain 1 element"
                });
        }
        TestRunner.AddResult (
            new TestRunResult () {
                CallerName = callerName,
                    CallerLine = callerLine.ToString (),
                    Success = true,
                    Assertion = "Single<T>"
            });
    }

    public static void Contains<T> (T token1, T token2, [CallerMemberName] string callerName = "", [CallerLineNumber] int callerLine = 0) {
        if (typeof (T) == typeof (System.String)) {
            if (!((token2 as string)).Contains (token1 as string)) {
                // throw new Exception ($"{token2} doesn't contain {token1}");
                TestRunner.AddResult (
                    new TestRunResult () {
                        CallerName = callerName,
                            CallerLine = callerLine.ToString (),
                            Success = false,
                            Assertion = "Contains<T>",
                            ErrorMessage = $"{token2} doesn't contain {token1}"
                    });
            } else {
                TestRunner.AddResult (
                    new TestRunResult () {
                        CallerName = callerName,
                            CallerLine = callerLine.ToString (),
                            Success = true,
                            Assertion = "Contains<T>"
                    });
            }
        } else {
            throw new Exception ("It is not possible to use .Contains() method");
        }
    }

    public static void All<T> (IEnumerable<T> collection, Func<T, bool> predicate, [CallerMemberName] string callerName = "", [CallerLineNumber] int callerLine = 0) {
        bool res = collection.All (predicate);
        var tr = new TestRunResult () {
                CallerName = callerName,
                    CallerLine = callerLine.ToString (),
                    Success = res,
                    Assertion = "All<T>"
            };
        TestRunner.AddResult (tr);
        if(!res) {
            tr.ErrorMessage = "Condition is not met for all members";
        }
    }

}

public static class TestRunner {
    public static List<TestRunResult> Results { get; } = new List<TestRunResult> ();

    public static void AddResult (TestRunResult res) {
        Results.Add (res);
    }

    public static void Print () {
        System.Console.WriteLine ("TestRunner.Print");
        System.Console.WriteLine ("============================================");
        foreach (var log in Results) {
            System.Console.WriteLine (log);
        }
        System.Console.WriteLine ("============================================");
    }
}

public class TestRunResult {
    public string CallerName { get; set; }
    public string CallerLine { get; set; }
    public string Assertion { get; set; }
    public bool Success { get; set; }
    public string ErrorMessage { get; set; }
    public override string ToString () {
        return $"Assertion: {Assertion, 15}; MethodName: {CallerName, 10}; Line: {CallerLine, 3}; " + (Success? $"Success: {Success}": $"ErrorMessage: {ErrorMessage}");
    }
}