FakeLocalizer.cs

using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using Microsoft.Extensions.Localization;

namespace BlogWeb.Tests.Fakes
{
    public class FakeLocalizer<T> : IStringLocalizer<T>, IFakeLocalizerBuilder<T>
    {
        private Func<string, string, string> indexWithValue;
        private IEnumerable<LocalizedString> allLocalizedStrings;

        public static IFakeLocalizerBuilder<T> MockNewLocalizer() => new FakeLocalizer<T>();

        public static IFakeLocalizerBuilder<T> MockNewLocalizer(IStringLocalizer<T> existing)
            => MockNewLocalizer()
                .UseIndex((name, value) => existing[name])
                .UseGetAllStrings(existing.GetAllStrings().ToArray());

        public static IStringLocalizer<T> DefaultLocalizer =>
            FakeLocalizer<T>.MockNewLocalizer().UseIndex((name, value) => value).Build();

        public LocalizedString this[string name]
        {
            get
            {
                if (indexWithValue != null)
                {
                    string localizedString = indexWithValue(name, name);
                    return new LocalizedString(localizedString, localizedString);
                }

                return new LocalizedString(name, name);
            }
        }

        public LocalizedString this[string name, params object[] arguments]
        {
            get
            {
                return this[name];
            }
        }

        public IEnumerable<LocalizedString> GetAllStrings(bool includeParentCultures) => this.allLocalizedStrings ?? Enumerable.Empty<LocalizedString>();

        public IStringLocalizer WithCulture(CultureInfo culture) => this;

        IFakeLocalizerBuilder<T> IFakeLocalizerBuilder<T>.UseGetAllStrings(params LocalizedString[] strings)
        {
            this.allLocalizedStrings = strings;
            return this;
        }

        IStringLocalizer<T> IFakeLocalizerBuilder<T>.Build() => this;

        IFakeLocalizerBuilder<T> IFakeLocalizerBuilder<T>.UseIndex(Func<string, string> indexerWithNamedValue)
        {
            this.indexWithValue = new Func<string, string, string>((name, value) => indexerWithNamedValue(name));
            return this;
        }

        IFakeLocalizerBuilder<T> IFakeLocalizerBuilder<T>.UseIndex(Func<string, string, string> IndexWithNameAndValue)
        {
            this.indexWithValue = IndexWithNameAndValue;
            return this;
        }
    }
}