Specflow by default generates the output results in SpecFlow JSON format. AssertThat plugin can consume it as Cucumber JSON format. The following solution will generate the output result in Cucumber JSON format in parallel and the result could imported to the AssertThat plugin using REST API for Jira Cloud or running a Command line tool.

Option 1 (.NET 4.5)

Step 1: Add Dependencies

https://www.nuget.org/packages/SpecNuts/
https://www.nuget.org/packages/SpecNuts.Json/

Step 2: Add the below code in .cs of feature file

[BeforeTestRun]
public static void BeforeTestRun() {
    SpecNuts.Reporters.Add(new JsonReporter());
 
    SpecNuts.Reporters.FinishedReport += (sender, args) => {
 
        String pathName = "specflow_cucumber.json";
 
        System.IO.File.WriteAllText(pathName, args.Reporter.WriteToString());
 
        Console.WriteLine("Result File: " + System.IO.Directory.GetCurrentDirectory().ToString() + System.IO.Path.DirectorySeparatorChar + pathName);
 
    };
}

Step 3: Open Text Explorer in Visual Studio by Test > Windows > Test Explorer -> Choose Run All

Step 4: In Visual Studio console, select show output from Test and open Report File as path given in Console

Step 5: The generated output result file will be in Cucumber JSON format with the name "specflow_cucumber.json". The generated JSON can be imported into the plugin now.

Option 2

Before compiling and running the tests, you have to use a proper SpecFlow report template file in order to generate a valid Cucumber JSON report and you have to configure the test profile to use it.

CucumberJson.cshtml 

@inherits TechTalk.SpecRun.Framework.Reporting.CustomTemplateBase<TestRunResult>
@using System
@using System.Collections.Generic
@using System.Linq
@using System.Globalization
@using Newtonsoft.Json
@using Newtonsoft.Json.Converters
@using TechTalk.SpecRun.Framework
@using TechTalk.SpecRun.Framework.Results
@using TechTalk.SpecRun.Framework.TestSuiteStructure
@using TechTalk.SpecRun.Framework.Tracing
@{
    var serializationSettings = new JsonSerializerSettings
    {
        ReferenceLoopHandling = ReferenceLoopHandling.Ignore,
        Converters = new List<JsonConverter>() { new StringEnumConverter(false) }
    };
 
    var features = GetTextFixtures()
        .Select(f => new
        {
            description = "",
            elements = (from scenario in f.SubNodes
                        let lastExecutionResult = GetTestItemResult(scenario.GetTestSequence().First()).LastExecutionResult()
                        select new
                        {
                            description = "",
                            id = "",
                            keyword = "Scenario",
                            line = scenario.Source.SourceLine + 1,
                            name = scenario.Title,
                            tags = scenario.Tags.Select(t => new { name = t, line = 1 }),
                            steps = from step in lastExecutionResult.Result.TraceEvents
                                    where IsRelevant(step) && (step.ResultType == TestNodeResultType.Succeeded || step.ResultType == TestNodeResultType.Failed || step.ResultType == TestNodeResultType.Pending)
                                    && (step.Type == TraceEventType.Test || step.Type == TraceEventType.TestAct || step.Type == TraceEventType.TestArrange || step.Type == TraceEventType.TestAssert)
                                    let keyword = step.StepBindingInformation == null ? "" : step.StepBindingInformation.StepInstanceInformation == null ? "" : step.StepBindingInformation.StepInstanceInformation.Keyword
                                    let matchLocation = step.StepBindingInformation == null ? "" : step.StepBindingInformation.MethodName
                                    let name = step.StepBindingInformation == null ? "" : step.StepBindingInformation.Text
                                    let cucumberStatus = step.ResultType == TestNodeResultType.Succeeded ? "Passed" : step.ResultType.ToString()
                                    select new
                                    {
                                        keyword = keyword,
                                        line = 0,
                                        match = new
                                        {
                                            location = matchLocation
                                        },
                                        name = name,
                                        result = new
                                        {
                                            duration = step.Duration.TotalMilliseconds,
                                            error_message = step.StackTrace,
                                            status = cucumberStatus
                                        }
                                    },
                            type = "scenario"
                        }).ToList(),
            id = "",
            keyword = "Feature",
            line = f.Source.SourceLine + 1,
            tags = f.Tags.Select(t => new { name = t, line = 1 }),
            name = f.Title,
            uri = f.Source.SourceFile
        });
}
@Raw(JsonConvert.SerializeObject(features, Formatting.Indented, serializationSettings))

Default.srprofile 

<?xml version="1.0" encoding="utf-8"?>
<TestProfile xmlns="http://www.specflow.org/schemas/plus/TestProfile/1.5">
  <Settings projectName="TestProject" projectId="{xxx-xxx-xxx-xxx}" />
  <Execution stopAfterFailures="2" testThreadCount="1" testSchedulingMode="Sequential" />
  <TestAssemblyPaths>
    <TestAssemblyPath>TestProject.dll</TestAssemblyPath>
  </TestAssemblyPaths>
  <DeploymentTransformation>
   ...
  </DeploymentTransformation>
 
  <Report>
    <Template name="CucumberJson.cshtml" outputName="data.json"/>
  </Report>
   
</TestProfile>

Tests can be run from within the IDE (e.g. Visual Studio) or by the command line; in the later case, make sure to specify the profile name and all the paths properly.

Since there is code-behind file generation, it is required to have the NuGet "SpecFlow.Tools.MsBuild.Generation" package.

msbuild /t:Clean;Rebuild
cd bin\debug
..\..\..\packages\SpecRun.Runner.1.7.2\tools\SpecRun.exe run Default.srprofile /outputFolder:..\..\..\TestResults
cd ..\..