Issue with automating 'Then' step BDD C# Specflow

I'm running a test where i'm validating an output from a file (e.g irm_xxx_lkdd_xuxt.csv.ovr) with my expected output "6677,6677_6677,3001,6"

The issue i'm having is my code below isn't being recognised by my specflow 'Then' step. I think the issue could be because i'm using Nunit testcase. Is there a way round this? or can i combine my file path and expected result within my ValidateMeasurement method

    [Then("Transfer measure should be generated for (.*)")]


[TestCase("irm_xxx_lkdd_xuxt.csv.ovr", "6677,6677_6677,3001,6")]
[TestCase("irm_xxx_lkdd_fcvt.csv.ovrr", "6677,6677_6677,3001,6")]
[TestCase("irm_xxx_lkdd_fbvt.csv.ovrr", "6677,6677_6677,3001,6")]

public void ValidateMeasurement(string path, string expected)
{
    const string processFilePath = "/orabin/app/product/inputs/ff/actuals/";
    var actual = Common.LinuxCommandExecutor
                       .RunLinuxcommand($"cat {processFilePath}{path}");

    Assert.AreEqual(expected, actual);

}