ApprovalTests DiffReporter is not popping up diff window when test is failed

ApprovalTests DiffReporter is not popping up diff window after running the test if the test is failed. Below is my code.

[UseReporter(typeof(DiffReporter))]
[TestClass]
public class ProjectEmployeeJsonTests
{
    [TestMethod]
    public void ToCommand()
    {
        var source = new EmployeeJson
        {
            firstName = "ABC",
            lastName = "TestCarrier"
        };

        var destination = new EmployeeCommand();
        var mapper = GetMapper();
        mapper.Execute(source, destination);

        Approvals.Verify(
            JsonConvert.SerializeObject(
                destination,
                Formatting.Indented));
    }
}

It pops up the diff window for the same code on one of my colleague's machine. We are using the same version of Visual studio with same settings and both of us do not have any diff tools installed.

Any help here would be highly appreciated. Thanks!