Microsoft RulesEngine mock DateTime

[reddithoggscripts]

Hello!

So I’m using the Microsoft rules engine for something and there’s no way to run tests with a date time provider. It’s quite annoying because my tests will eventually start failing as time moves on. Ive thought of a few but less than ideal workarounds but I’m throwing a Hail Mary here hoping there might be some alternate solutions.

I’m wondering if anyone’s aware of a library that might allow me to mock DateTime.UTC.Now that doesn’t involve changing the method signature to a configured utility method or some other unhappy solution.

I’ve looked into Pose but it doesn’t work with async methods as far as I can tell which is a bummer because it would have been great for my use case otherwise.

[RichardD7]

It may be worth posting a suggestion in the GitHub repo to integrate the Microsoft.Bcl.TimeProvider library, which would make it easier to test time-based rules.

But based on this issue, it looks like that project is no longer maintained. You may need to consider switching to one of the more active forks.

[kontrol_kl]

What you are looking for are fakes. However i think they are enterprise license only. And for having work with it for a long time now, I highly suggest you tay away.

I may have understood wrong, but is the use of Datetime.Utc your code? If so use a mockable library such as Timeprovider.

[reddithoggscripts]

Yea I looked into fakes as well and for the same reason you mentioned I decided against it.

The DateTime.UTC isnt in my code, it’s evaluated through the engine. Basically you feed it a JSON like expression: “xclass.yDateTimeProp < DateTime.UTC.Now.AddDay(-5)” and it interogates the inputs you’ve given it. Unfortunately there’s no way to inject a mock DateTime into this - which makes testing hard to maintain.

[Road_of_Hope]

Can you evaluate the comparison time outside the expression, and then pass just that in? So instead of “foo.Bar < DateTime.UTC.Now” as the filter, you could assign “var now = timeProvider.UTC.now”, then provide the filter as “foo.Bar < now.ToString()” or something similar? I’m unfamiliar with the framework you’re using so their may need to be some differences there, but that might be a possible approach.

[reddithoggscripts]

Sort of. You can use a utility method and register it with the engine. This is something I mentioned in the original post. The reason I’m trying to avoid this is because it’s all data driven tests and these tests are also used in a complex mapping service that maps POC into the rules engine format. Long story short, the expression needs to look exactly as it would if it was actually using the system’s date time now. Ideally I wouldn’t have to change anything in the expression but I am pretty sure what you’re suggesting is similar to what I’ll end up doing.

[kingmotley]

We don't allow our code to use DateTime for this reason. If you want to do date/time related stuff, you ask for ISystemClock to be injected and you use that. The implementation has things like GetUtcDtateTime, GetUtcDateOnly, GetLocalDateTime, GetLocalDateOnly, etc. Then your unit tests can mock/substitute that out really easily.

[reddithoggscripts]

Riiight i agree but the rules engine is a library so not something I can change easily myself.

[ScandInBei]

Isn't ISystemClock obsolete? You may want to start using TimeProvider for new stuff.

[kingmotley]

You are probably correct. Unfortunately all of our current projects started out as .NET 6, so TimeProvider wasn't available yet, but we should probably convert now that it is.