TestsTemplate.cs

public class MyClassTests
{
    public class Method1 : MyClassTestsBase
    {
        [Theory]
        [AutoData]
        public async Task Should_return_A_when_X(parameters)
        {
            //! Arrange
            // ...

            //! Act
            // ...

            //! Assert
            // ...
        }

        [Theory]
        [AutoData]
        public async Task Should_throw_B_when_Y(parameters)
        {
            //! Arrange
            // ...

            //! Act
            // ...

            //! Assert
            // ...
        }
    }

    public class Method2 : MyClassTestsBase
    {
        [Fact]
        public async Task Should_return_A_when_X()
        {
            //! Arrange
            // ...

            //! Act
            // ...

            //! Assert
            // ...
        }

        [Fact]
        public async Task Should_throw_B_when_Y()
        {
            //! Arrange
            // ...

            //! Act
            // ...

            //! Assert
            // ...
        }
    }

    public abstract class MyClassTestsBase
    {
        protected readonly MyClass Instance;
        protected readonly IDependency1 Dependency1;
        protected readonly IDependency2 Dependency2;

        protected UserManagerTestsBase()
        {
            Dependency1 = Substitute.For<IDependency1>();
            Dependency2 = Substitute.For<IDependency2>();
            Instance = new MyClass(IDependency1, IDependency2);
        }
    }
}