MathsCustomerTests.cs

using System;
using System.Collections.Generic;
using System.Data.OleDb;
using System.Reflection;
using NUnit.Framework;

namespace Excel.CustomerTests
{
    [TestFixture]
    public class MathsCustomerTests
    {
        [Test, TestCaseSource(typeof (ExcelDataSource), "Data")]
        public void SquareRoot(string number, string tolerance, string squareRoot)
        {
            Assert.That(Maths.SquareRoot(ToDouble(number)),
                Is.EqualTo(ToDouble(squareRoot)).Within(ToDouble(tolerance)));
        }

        private double ToDouble(string squareRoot)
        {
            return Double.Parse(squareRoot);
        }
    }

    public class Maths
    {
        public static double SquareRoot(double number)
        {
            return Math.Sqrt(number);
        }
    }

    internal class ExcelDataSource
    {
        private static readonly string binPath = Assembly.GetCallingAssembly().CodeBase;

        private static readonly string projectPath =
            new Uri(binPath.Substring(0, binPath.LastIndexOf("bin", StringComparison.Ordinal))).LocalPath;

        public IEnumerable<TestCaseData> Data
        {
            get
            {
                var connectString =
                    string.Format(
                        "Provider=Microsoft.ACE.OLEDB.12.0;Data Source={0};Extended Properties=\"Excel 12.0 Xml;HDR=YES\";",
                        projectPath + "customerdata.xlsx");
                var connection = new OleDbConnection(connectString);
                connection.Open();
                var command = new OleDbCommand("SELECT * FROM [examples]", connection);
                var reader = command.ExecuteReader();
                var testCases = new List<TestCaseData>();
                while (reader.Read())
                {
                    var row = new List<string>();
                    for (var i = 0; i < reader.FieldCount; i++)
                        row.Add(reader.GetValue(i).ToString());
                    testCases.Add(new TestCaseData(row.ToArray()));
                }
                return testCases;
            }
        }
    }
}

Hi Jason, I enjoyed your blog post about this, and have done something similar (generating BDD / C# tests from Excel), which maybe you'll find ineteresting :)
https://dev.to/ceddlyburge/introducing-customertestsexcel-4f7b