How can I compare a non-nullable bool with a nullable bool using Shouldly without explicit casts?

When using Shouldly’s ShouldBe method, the generic type T is inferred from the expected value. In your case, because graphUsers[0].AccountEnabled is a bool? (nullable bool), T is bool? and both actual and expected are expected to be of that type. Since o[0].AccountEnabled is a bool (non‐nullable), you have to explicitly convert it to bool? so that the types match.

Why the Explicit Cast is Necessary

Shouldly defines the extension method like this:

CSHARPCopied
public static void ShouldBe<T>(
    this T? actual,
    T? expected,
    string? customMessage = null)
{
    // ...
}

When expected is of type bool?, the compiler attempts to bind the extension method so that both parameters are bool?. Because o[0].AccountEnabled is a bool, it doesn’t automatically have the extension method ShouldBe(bool?, bool?, string?) (as the receiver), so you must cast it by writing:

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((bool?)o[0].AccountEnabled).ShouldBe(graphUsers[0].AccountEnabled);

This cast is a lifted conversion: a non-nullable bool converts to a nullable bool without any extra wrapping (it simply becomes a bool? with the same true or false value). It doesn’t “double-wrap” the value (i.e. you won’t get something like a bool??).

Comparing Non‑Nullable and Nullable Types

If you prefer not to write an explicit cast every time, you have a couple of options:

1. Cast the expected value instead:
   If you are certain that the non‑nullable value should compare equal to the nullable one (and you don’t need to check for null), you could write:

   CSHARPCopied
   o[0].AccountEnabled.ShouldBe(graphUsers[0].AccountEnabled.GetValueOrDefault());

   Note that this works only if you are comfortable comparing with a default value (false) when graphUsers[0].AccountEnabled is null.

2. Create a helper extension method:
   You might wrap the conversion in your own extension helper:

   CSHARPCopied
   public static void ShouldBeSameAs(this bool actual, bool? expected, string? customMessage = null)
   {
       ((bool?)actual).ShouldBe(expected, customMessage);
   }

   Then your test code becomes:

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   o[0].AccountEnabled.ShouldBeSameAs(graphUsers[0].AccountEnabled);

In summary, the explicit nullable cast is required because Shouldly’s ShouldBe method demands that both values be of the same type (bool? in this case). The cast (bool?) converts a bool to a nullable bool by “lifting” the value—there is no concept of a “double nullable” (bool??).