Make Pulumi.RunException assertable

[JasonWhall]

Hello!

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Issue details

Currently when writing Unit tests for a stack that does Pulumi.Log.Error(""). The resulting stack will throw a Pulumi.RunException in the deployment runner. As this is an internal only type currently, we are unable to assert to check this error has been thrown. The workaround currently is to assert on the Exception type, but isn't accurate to the type of exception thrown. Below shows an example of a test that would check for this:

using FluentAssertions;
using NSubstitute;
using Pulumi;
using Pulumi.Testing;

public class UnitTest1
{

    [Fact]
    public async Task Stack_LoggingError_ShouldThrowExpectedException()
    {
        // Arrange
        var mocks = Substitute.For<IMocks>();
        var options = new TestOptions { IsPreview = false };
        static void act()
        {
            Log.Error("Message 1");
        };

        var sut = () => Deployment.TestAsync(mocks, options, act);

        // Act & Assert
        await sut.Should().ThrowAsync<Exception>()
            .WithMessage("Message 1");

        // Desired
        /*
            await sut.Should().ThrowAsync<Pulumi.RunException>()
                .WithMessage("Message 1");
        */
    }
}

Could the RunException be made public so we can assert on this?

Affected area/feature

Pulumi Core

[justinvp]

Thanks for the suggestion, @JasonWhall. I don't recall if we had a good reason for making RunException internal, other than not intending it to be thrown by users. But I understand why it'd be nice to write a test like this.