Practical shift-left on testing

Should You Unit-Test in ASP.NET Core?

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What should be the SUT in tests when you do shift-left on testing?

The Startup pattern, larger units, fewer test doubles and a bit of BDD thinking.

Let’s see what happens if we write isolated, in-memory tests but avoid substituting production code with test doubles as much as possible.

Wait, but why?

Most unit tests are not real tests!

Show me the code

The two AddSingleton statements register two facade interfaces representing the external dependencies. The AddControllers statement registers a group of dependencies; this is a commonly used pattern.
The Startup class is referenced in our service entry point with webBuilder.UseStartup<Startup>.
This will replace our two external dependencies from production code with two test doubles in test code.
The Startup class is referenced in the in our test project entry point with new WebApplicationFactory<Startup>.

If you find that you can follow the dogma rule, then you are in a good position for shift-left on testing.

Conclusion

It is an important goal of testing to learn more about the code and how it works.

Rather than having an inside-out or outside-in approach when you do your steps, try to do both.

The Startup

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