Below is a summary of tools/libraries I have used to build maintainable suite of auto tests on large ecom project.

While it is hard to start without test framework :), some autaaof the libraries listed below could be easily omitted by developers.

XUnit

xUnit.net is a developer testing framework, built to support Test Driven Development, with a design goal of extreme simplicity and alignment with framework features. (copied from nuget package description)

AutoFixture

AutoFixture makes it easier for developers to do Test-Driven Development by automating non-relevant Test Fixture Setup, allowing the Test Developer to focus on the essentials of each test case. (copied from nuget package description)

I could not stress enough how useful the library is. It allows to greatly decrease the lines of code for your test suits and make tests more readable.

FluentAssertions

A very extensive set of extension methods that allow you to more naturally specify the expected outcome of a TDD or BDD-style unit test. (copied from nuget package description)

It providesa a lot more possibilities to assert the test outcome than standard test frameworks do.

Simple.Data.SqlServer

Simple.Data is a lightweight framework that uses the dynamic features of .NET 4 to provide an expressive, ORM-ish way of accessing and manipulating data without any of the code pre-generation and boilerplate required by other frameworks. (copied from nuget package description)

Greatly could help when need to quickly verify the test that makes side effects in DB. Or perform test data setup.