// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc.ModelBinding;
using Microsoft.AspNetCore.Mvc.Rendering;
using Microsoft.AspNetCore.Mvc.Routing;
using Microsoft.AspNetCore.Razor.TagHelpers;
using Microsoft.AspNetCore.Routing;
using Moq;
using Xunit;

namespace Microsoft.AspNetCore.Mvc.TagHelpers
{
    public class FormActionTagHelperTest
    {
        [Fact]
        public async Task ProcessAsync_GeneratesExpectedOutput()
        {
            // Arrange
            var expectedTagName = "not-button-or-submit";
            var metadataProvider = new TestModelMetadataProvider();

            var tagHelperContext = new TagHelperContext(
                tagName: "form-action",
                allAttributes: new TagHelperAttributeList
                {
                    { "id", "my-id" },
                },
                items: new Dictionary<object, object>(),
                uniqueId: "test");
            var output = new TagHelperOutput(
                expectedTagName,
                attributes: new TagHelperAttributeList
                {
                    { "id", "my-id" },
                },
                getChildContentAsync: (useCachedResult, encoder) =>
                {
                    var tagHelperContent = new DefaultTagHelperContent();
                    tagHelperContent.SetContent("Something Else");  // ignored
                    return Task.FromResult<TagHelperContent>(tagHelperContent);
                });

            var urlHelper = new Mock<IUrlHelper>(MockBehavior.Strict);
            urlHelper
                .Setup(mock => mock.Action(It.IsAny<UrlActionContext>()))
                .Returns<UrlActionContext>(c => $"{c.Controller}/{c.Action}/{(c.Values as RouteValueDictionary)["name"]}");

            var viewContext = new ViewContext();
            var urlHelperFactory = new Mock<IUrlHelperFactory>(MockBehavior.Strict);
            urlHelperFactory
                .Setup(f => f.GetUrlHelper(viewContext))
                .Returns(urlHelper.Object);

            var tagHelper = new FormActionTagHelper(urlHelperFactory.Object)
            {
                Action = "index",
                Controller = "home",
                RouteValues =
                {
                    {  "name", "value" },
                },
                ViewContext = viewContext,
            };

            // Act
            await tagHelper.ProcessAsync(tagHelperContext, output);

            // Assert
            Assert.Collection(
                output.Attributes,
                attribute =>
                {
                    Assert.Equal("id", attribute.Name, StringComparer.Ordinal);
                    Assert.Equal("my-id", attribute.Value as string, StringComparer.Ordinal);
                },
                attribute =>
                {
                    Assert.Equal("formaction", attribute.Name, StringComparer.Ordinal);
                    Assert.Equal("home/index/value", attribute.Value as string, StringComparer.Ordinal);
                });
            Assert.False(output.IsContentModified);
            Assert.False(output.PostContent.IsModified);
            Assert.False(output.PostElement.IsModified);
            Assert.False(output.PreContent.IsModified);
            Assert.False(output.PreElement.IsModified);
            Assert.Equal(TagMode.StartTagAndEndTag, output.TagMode);
            Assert.Equal(expectedTagName, output.TagName);
        }

        [Fact]
        public async Task ProcessAsync_GeneratesExpectedOutput_WithRoute()
        {
            // Arrange
            var expectedTagName = "not-button-or-submit";
            var metadataProvider = new TestModelMetadataProvider();

            var tagHelperContext = new TagHelperContext(
                tagName: "form-action",
                allAttributes: new TagHelperAttributeList
                {
                    { "id", "my-id" },
                },
                items: new Dictionary<object, object>(),
                uniqueId: "test");
            var output = new TagHelperOutput(
                expectedTagName,
                attributes: new TagHelperAttributeList
                {
                    { "id", "my-id" },
                },
                getChildContentAsync: (useCachedResult, encoder) =>
                {
                    var tagHelperContent = new DefaultTagHelperContent();
                    tagHelperContent.SetContent("Something Else");  // ignored
                    return Task.FromResult<TagHelperContent>(tagHelperContent);
                });

            var urlHelper = new Mock<IUrlHelper>(MockBehavior.Strict);
            urlHelper
                .Setup(mock => mock.RouteUrl(It.IsAny<UrlRouteContext>()))
                .Returns<UrlRouteContext>(c => $"{c.RouteName}/{(c.Values as RouteValueDictionary)["name"]}");

            var viewContext = new ViewContext();
            var urlHelperFactory = new Mock<IUrlHelperFactory>(MockBehavior.Strict);
            urlHelperFactory
                .Setup(f => f.GetUrlHelper(viewContext))
                .Returns(urlHelper.Object);

            var tagHelper = new FormActionTagHelper(urlHelperFactory.Object)
            {
                Route = "routine",
                RouteValues =
                {
                    {  "name", "value" },
                },
                ViewContext = viewContext,
            };

            // Act
            await tagHelper.ProcessAsync(tagHelperContext, output);

            // Assert
            Assert.Collection(
                output.Attributes,
                attribute =>
                {
                    Assert.Equal("id", attribute.Name, StringComparer.Ordinal);
                    Assert.Equal("my-id", attribute.Value as string, StringComparer.Ordinal);
                },
                attribute =>
                {
                    Assert.Equal("formaction", attribute.Name, StringComparer.Ordinal);
                    Assert.Equal("routine/value", attribute.Value as string, StringComparer.Ordinal);
                });
            Assert.False(output.IsContentModified);
            Assert.False(output.PostContent.IsModified);
            Assert.False(output.PostElement.IsModified);
            Assert.False(output.PreContent.IsModified);
            Assert.False(output.PreElement.IsModified);
            Assert.Equal(TagMode.StartTagAndEndTag, output.TagMode);
            Assert.Equal(expectedTagName, output.TagName);
        }

        // RouteValues property value, expected RouteValuesDictionary content.
        public static TheoryData<IDictionary<string, string>, IDictionary<string, object>> RouteValuesData
        {
            get
            {
                return new TheoryData<IDictionary<string, string>, IDictionary<string, object>>
                {
                    { null, null },
                    // FormActionTagHelper ignores an empty route values dictionary.
                    { new Dictionary<string, string>(), null },
                    {
                        new Dictionary<string, string> { { "name", "value" } },
                        new Dictionary<string, object> { { "name", "value" } }
                    },
                    {
                        new SortedDictionary<string, string>(StringComparer.Ordinal)
                        {
                            { "name1", "value1" },
                            { "name2", "value2" },
                        },
                        new SortedDictionary<string, object>(StringComparer.Ordinal)
                        {
                            { "name1", "value1" },
                            { "name2", "value2" },
                        }
                    },
                };
            }
        }

        [Theory]
        [MemberData(nameof(RouteValuesData))]
        public async Task ProcessAsync_CallsActionWithExpectedParameters(
            IDictionary<string, string> routeValues,
            IDictionary<string, object> expectedRouteValues)
        {
            // Arrange
            var context = new TagHelperContext(
                tagName: "form-action",
                allAttributes: new TagHelperAttributeList(),
                items: new Dictionary<object, object>(),
                uniqueId: "test");
            var output = new TagHelperOutput(
                "button",
                attributes: new TagHelperAttributeList(),
                getChildContentAsync: (useCachedResult, encoder) =>
                {
                    return Task.FromResult<TagHelperContent>(new DefaultTagHelperContent());
                });

            var urlHelper = new Mock<IUrlHelper>(MockBehavior.Strict);
            urlHelper
                .Setup(mock => mock.Action(It.IsAny<UrlActionContext>()))
                .Callback<UrlActionContext>(param =>
                {
                    Assert.Equal("delete", param.Action, StringComparer.Ordinal);
                    Assert.Equal("books", param.Controller, StringComparer.Ordinal);
                    Assert.Equal("test", param.Fragment, StringComparer.Ordinal);
                    Assert.Null(param.Host);
                    Assert.Null(param.Protocol);
                    Assert.Equal<KeyValuePair<string, object>>(expectedRouteValues, param.Values as RouteValueDictionary);
                })
                .Returns("home/index");

            var viewContext = new ViewContext();
            var urlHelperFactory = new Mock<IUrlHelperFactory>(MockBehavior.Strict);
            urlHelperFactory
                .Setup(f => f.GetUrlHelper(viewContext))
                .Returns(urlHelper.Object);

            var tagHelper = new FormActionTagHelper(urlHelperFactory.Object)
            {
                Action = "delete",
                Controller = "books",
                Fragment = "test",
                RouteValues = routeValues,
                ViewContext = viewContext,
            };

            // Act
            await tagHelper.ProcessAsync(context, output);

            // Assert
            Assert.Equal("button", output.TagName);
            var attribute = Assert.Single(output.Attributes);
            Assert.Equal("formaction", attribute.Name);
            Assert.Equal("home/index", attribute.Value);
            Assert.Empty(output.Content.GetContent());
        }

        [Theory]
        [MemberData(nameof(RouteValuesData))]
        public async Task ProcessAsync_CallsRouteUrlWithExpectedParameters(
            IDictionary<string, string> routeValues,
            IDictionary<string, object> expectedRouteValues)
        {
            // Arrange
            var context = new TagHelperContext(
                tagName: "form-action",
                allAttributes: new TagHelperAttributeList(),
                items: new Dictionary<object, object>(),
                uniqueId: "test");
            var output = new TagHelperOutput(
                "button",
                attributes: new TagHelperAttributeList(),
                getChildContentAsync: (useCachedResult, encoder) =>
                {
                    return Task.FromResult<TagHelperContent>(new DefaultTagHelperContent());
                });

            var urlHelper = new Mock<IUrlHelper>(MockBehavior.Strict);
            urlHelper
                .Setup(mock => mock.RouteUrl(It.IsAny<UrlRouteContext>()))
                .Callback<UrlRouteContext>(param =>
                {
                    Assert.Null(param.Host);
                    Assert.Null(param.Protocol);
                    Assert.Equal("test", param.Fragment, StringComparer.Ordinal);
                    Assert.Equal("Default", param.RouteName, StringComparer.Ordinal);
                    Assert.Equal<KeyValuePair<string, object>>(expectedRouteValues, param.Values as RouteValueDictionary);
                })
                .Returns("home/index");

            var viewContext = new ViewContext();
            var urlHelperFactory = new Mock<IUrlHelperFactory>(MockBehavior.Strict);
            urlHelperFactory
                .Setup(f => f.GetUrlHelper(viewContext))
                .Returns(urlHelper.Object);

            var tagHelper = new FormActionTagHelper(urlHelperFactory.Object)
            {
                Route = "Default",
                Fragment = "test",
                RouteValues = routeValues,
                ViewContext = viewContext,
            };

            // Act
            await tagHelper.ProcessAsync(context, output);

            // Assert
            Assert.Equal("button", output.TagName);
            var attribute = Assert.Single(output.Attributes);
            Assert.Equal("formaction", attribute.Name);
            Assert.Equal("home/index", attribute.Value);
            Assert.Empty(output.Content.GetContent());
        }

        // Area property value, RouteValues property value, expected "area" in final RouteValuesDictionary.
        public static TheoryData<string, Dictionary<string, string>, string> AreaRouteValuesData
        {
            get
            {
                return new TheoryData<string, Dictionary<string, string>, string>
                {
                    { "Area", null, "Area" },
                    // Explicit Area overrides value in the dictionary.
                    { "Area", new Dictionary<string, string> { { "area", "Home" } }, "Area" },
                    // Empty string is also passed through to the helper.
                    { string.Empty, null, string.Empty },
                    { string.Empty, new Dictionary<string, string> { { "area", "Home" } }, string.Empty },
                    // Fall back "area" entry in the provided route values if Area is null.
                    { null, new Dictionary<string, string> { { "area", "Admin" } }, "Admin" },
                };
            }
        }

        [Theory]
        [MemberData(nameof(AreaRouteValuesData))]
        public async Task ProcessAsync_CallsActionWithExpectedRouteValues(
            string area,
            Dictionary<string, string> routeValues,
            string expectedArea)
        {
            // Arrange
            var context = new TagHelperContext(
                tagName: "form-action",
                allAttributes: new TagHelperAttributeList(),
                items: new Dictionary<object, object>(),
                uniqueId: "test");
            var output = new TagHelperOutput(
                "submit",
                attributes: new TagHelperAttributeList(),
                getChildContentAsync: (useCachedResult, encoder) =>
                {
                    return Task.FromResult<TagHelperContent>(new DefaultTagHelperContent());
                });

            var expectedRouteValues = new Dictionary<string, object> { { "area", expectedArea } };
            var urlHelper = new Mock<IUrlHelper>(MockBehavior.Strict);
            urlHelper
                .Setup(mock => mock.Action(It.IsAny<UrlActionContext>()))
                .Callback<UrlActionContext>(param => Assert.Equal(expectedRouteValues, param.Values as RouteValueDictionary))
                .Returns("admin/dashboard/index");

            var viewContext = new ViewContext();
            var urlHelperFactory = new Mock<IUrlHelperFactory>(MockBehavior.Strict);
            urlHelperFactory
                .Setup(f => f.GetUrlHelper(viewContext))
                .Returns(urlHelper.Object);

            var tagHelper = new FormActionTagHelper(urlHelperFactory.Object)
            {
                Action = "Index",
                Area = area,
                Controller = "Dashboard",
                RouteValues = routeValues,
                ViewContext = viewContext,
            };

            // Act
            await tagHelper.ProcessAsync(context, output);

            // Assert
            Assert.Equal("submit", output.TagName);
            var attribute = Assert.Single(output.Attributes);
            Assert.Equal("formaction", attribute.Name);
            Assert.Equal("admin/dashboard/index", attribute.Value);
            Assert.Empty(output.Content.GetContent());
        }

        [Theory]
        [MemberData(nameof(AreaRouteValuesData))]
        public async Task ProcessAsync_CallsRouteUrlWithExpectedRouteValues(
            string area,
            Dictionary<string, string> routeValues,
            string expectedArea)
        {
            // Arrange
            var context = new TagHelperContext(
                tagName: "form-action",
                allAttributes: new TagHelperAttributeList(),
                items: new Dictionary<object, object>(),
                uniqueId: "test");
            var output = new TagHelperOutput(
                "submit",
                attributes: new TagHelperAttributeList(),
                getChildContentAsync: (useCachedResult, encoder) =>
                {
                    return Task.FromResult<TagHelperContent>(new DefaultTagHelperContent());
                });

            var expectedRouteValues = new Dictionary<string, object> { { "area", expectedArea } };
            var urlHelper = new Mock<IUrlHelper>(MockBehavior.Strict);
            urlHelper
                .Setup(mock => mock.RouteUrl(It.IsAny<UrlRouteContext>()))
                .Callback<UrlRouteContext>(param => Assert.Equal(expectedRouteValues, param.Values as RouteValueDictionary))
                .Returns("admin/dashboard/index");

            var viewContext = new ViewContext();
            var urlHelperFactory = new Mock<IUrlHelperFactory>(MockBehavior.Strict);
            urlHelperFactory
                .Setup(f => f.GetUrlHelper(viewContext))
                .Returns(urlHelper.Object);

            var tagHelper = new FormActionTagHelper(urlHelperFactory.Object)
            {
                Area = area,
                Route = "routine",
                RouteValues = routeValues,
                ViewContext = viewContext,
            };

            // Act
            await tagHelper.ProcessAsync(context, output);

            // Assert
            Assert.Equal("submit", output.TagName);
            var attribute = Assert.Single(output.Attributes);
            Assert.Equal("formaction", attribute.Name);
            Assert.Equal("admin/dashboard/index", attribute.Value);
            Assert.Empty(output.Content.GetContent());
        }

        [Fact]
        public async Task ProcessAsync_WithPageAndArea_CallsUrlHelperWithExpectedValues()
        {
            // Arrange
            var context = new TagHelperContext(
                tagName: "form-action",
                allAttributes: new TagHelperAttributeList(),
                items: new Dictionary<object, object>(),
                uniqueId: "test");
            var output = new TagHelperOutput(
                "submit",
                attributes: new TagHelperAttributeList(),
                getChildContentAsync: (useCachedResult, encoder) =>
                {
                    return Task.FromResult<TagHelperContent>(new DefaultTagHelperContent());
                });

            var urlHelper = new Mock<IUrlHelper>();
            urlHelper
                .Setup(mock => mock.RouteUrl(It.IsAny<UrlRouteContext>()))
                .Callback<UrlRouteContext>(routeContext =>
                {
                    var rvd = Assert.IsType<RouteValueDictionary>(routeContext.Values);
                    Assert.Collection(
                        rvd.OrderBy(item => item.Key),
                        item =>
                        {
                            Assert.Equal("area", item.Key);
                            Assert.Equal("test-area", item.Value);
                        },
                        item =>
                        {
                            Assert.Equal("page", item.Key);
                            Assert.Equal("/my-page", item.Value);
                        });
                })
                .Returns("admin/dashboard/index")
                .Verifiable();

            var viewContext = new ViewContext
            {
                RouteData = new RouteData(),
            };

            urlHelper.SetupGet(h => h.ActionContext)
                .Returns(viewContext);
            var urlHelperFactory = new Mock<IUrlHelperFactory>(MockBehavior.Strict);
            urlHelperFactory
                .Setup(f => f.GetUrlHelper(viewContext))
                .Returns(urlHelper.Object);

            var tagHelper = new FormActionTagHelper(urlHelperFactory.Object)
            {
                Area = "test-area",
                Page = "/my-page",
                ViewContext = viewContext,
            };

            // Act
            await tagHelper.ProcessAsync(context, output);

            // Assert
            urlHelper.Verify();
        }

        [Theory]
        [InlineData("button", "Action")]
        [InlineData("button", "Controller")]
        [InlineData("button", "Route")]
        [InlineData("button", "asp-route-")]
        [InlineData("submit", "Action")]
        [InlineData("submit", "Controller")]
        [InlineData("submit", "Route")]
        [InlineData("submit", "asp-route-")]
        public async Task ProcessAsync_ThrowsIfFormActionConflictsWithBoundAttributes(string tagName, string propertyName)
        {
            // Arrange
            var urlHelperFactory = new Mock<IUrlHelperFactory>().Object;

            var tagHelper = new FormActionTagHelper(urlHelperFactory);

            var output = new TagHelperOutput(
                tagName,
                attributes: new TagHelperAttributeList
                {
                    { "formaction", "my-action" }
                },
                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(null));
            if (propertyName == "asp-route-")
            {
                tagHelper.RouteValues.Add("name", "value");
            }
            else
            {
                typeof(FormActionTagHelper).GetProperty(propertyName).SetValue(tagHelper, "Home");
            }

            var expectedErrorMessage = $"Cannot override the 'formaction' attribute for <{tagName}>. <{tagName}> " +
                "elements with a specified 'formaction' must not have attributes starting with 'asp-route-' or an " +
                "'asp-action', 'asp-controller', 'asp-area', 'asp-fragment', 'asp-route', 'asp-page' or 'asp-page-handler' attribute.";

            var context = new TagHelperContext(
                tagName: "form-action",
                allAttributes: new TagHelperAttributeList(
                    Enumerable.Empty<TagHelperAttribute>()),
                items: new Dictionary<object, object>(),
                uniqueId: "test");

            // Act & Assert
            var ex = await Assert.ThrowsAsync<InvalidOperationException>(() => tagHelper.ProcessAsync(context, output));

            Assert.Equal(expectedErrorMessage, ex.Message);
        }

        [Theory]
        [InlineData("button", "Action")]
        [InlineData("button", "Controller")]
        [InlineData("submit", "Action")]
        [InlineData("submit", "Controller")]
        public async Task ProcessAsync_ThrowsIfRouteAndActionOrControllerProvided(string tagName, string propertyName)
        {
            // Arrange
            var urlHelperFactory = new Mock<IUrlHelperFactory>().Object;

            var tagHelper = new FormActionTagHelper(urlHelperFactory)
            {
                Route = "Default",
            };

            typeof(FormActionTagHelper).GetProperty(propertyName).SetValue(tagHelper, "Home");
            var output = new TagHelperOutput(
                tagName,
                attributes: new TagHelperAttributeList(),
                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(null));
            var expectedErrorMessage = string.Join(
                Environment.NewLine,
                $"Cannot determine the 'formaction' attribute for <{tagName}>. The following attributes are mutually exclusive:",
                "asp-route",
                "asp-controller, asp-action",
                "asp-page, asp-page-handler");

            var context = new TagHelperContext(
                tagName: "form-action",
                allAttributes: new TagHelperAttributeList(
                    Enumerable.Empty<TagHelperAttribute>()),
                items: new Dictionary<object, object>(),
                uniqueId: "test");

            // Act & Assert
            var ex = await Assert.ThrowsAsync<InvalidOperationException>(() => tagHelper.ProcessAsync(context, output));

            Assert.Equal(expectedErrorMessage, ex.Message);
        }

        [Theory]
        [InlineData("button")]
        [InlineData("submit")]
        public async Task ProcessAsync_ThrowsIfRouteAndPageProvided(string tagName)
        {
            // Arrange
            var urlHelperFactory = new Mock<IUrlHelperFactory>().Object;

            var tagHelper = new FormActionTagHelper(urlHelperFactory)
            {
                Route = "Default",
                Page = "Page",
            };

            var output = new TagHelperOutput(
                tagName,
                attributes: new TagHelperAttributeList(),
                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(null));
            var expectedErrorMessage = string.Join(
                Environment.NewLine,
                $"Cannot determine the 'formaction' attribute for <{tagName}>. The following attributes are mutually exclusive:",
                "asp-route",
                "asp-controller, asp-action",
                "asp-page, asp-page-handler");

            var context = new TagHelperContext(
                tagName: "form-action",
                allAttributes: new TagHelperAttributeList(
                    Enumerable.Empty<TagHelperAttribute>()),
                items: new Dictionary<object, object>(),
                uniqueId: "test");

            // Act & Assert
            var ex = await Assert.ThrowsAsync<InvalidOperationException>(() => tagHelper.ProcessAsync(context, output));

            Assert.Equal(expectedErrorMessage, ex.Message);
        }

        [Theory]
        [InlineData("button")]
        [InlineData("submit")]
        public async Task ProcessAsync_ThrowsIfRouteAndPageHandlerProvided(string tagName)
        {
            // Arrange
            var urlHelperFactory = new Mock<IUrlHelperFactory>().Object;

            var tagHelper = new FormActionTagHelper(urlHelperFactory)
            {
                Route = "Default",
                PageHandler = "PageHandler",
            };

            var output = new TagHelperOutput(
                tagName,
                attributes: new TagHelperAttributeList(),
                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(null));
            var expectedErrorMessage = string.Join(
                Environment.NewLine,
                $"Cannot determine the 'formaction' attribute for <{tagName}>. The following attributes are mutually exclusive:",
                "asp-route",
                "asp-controller, asp-action",
                "asp-page, asp-page-handler");

            var context = new TagHelperContext(
                tagName: "form-action",
                allAttributes: new TagHelperAttributeList(
                    Enumerable.Empty<TagHelperAttribute>()),
                items: new Dictionary<object, object>(),
                uniqueId: "test");

            // Act & Assert
            var ex = await Assert.ThrowsAsync<InvalidOperationException>(() => tagHelper.ProcessAsync(context, output));

            Assert.Equal(expectedErrorMessage, ex.Message);
        }

        [Theory]
        [InlineData("button")]
        [InlineData("submit")]
        public async Task ProcessAsync_ThrowsIfActionAndPageProvided(string tagName)
        {
            // Arrange
            var urlHelperFactory = new Mock<IUrlHelperFactory>().Object;

            var tagHelper = new FormActionTagHelper(urlHelperFactory)
            {
                Action = "Default",
                Page = "Page",
            };

            var output = new TagHelperOutput(
                tagName,
                attributes: new TagHelperAttributeList(),
                getChildContentAsync: (useCachedResult, encoder) => Task.FromResult<TagHelperContent>(null));
            var expectedErrorMessage = string.Join(
                Environment.NewLine,
                $"Cannot determine the 'formaction' attribute for <{tagName}>. The following attributes are mutually exclusive:",
                "asp-route",
                "asp-controller, asp-action",
                "asp-page, asp-page-handler");

            var context = new TagHelperContext(
                tagName: "form-action",
                allAttributes: new TagHelperAttributeList(
                    Enumerable.Empty<TagHelperAttribute>()),
                items: new Dictionary<object, object>(),
                uniqueId: "test");

            // Act & Assert
            var ex = await Assert.ThrowsAsync<InvalidOperationException>(() => tagHelper.ProcessAsync(context, output));

            Assert.Equal(expectedErrorMessage, ex.Message);
        }
    }
}