public void ResolveExtensions() { var extDefn = source.GetExtensionDefinition("http://hl7.org/fhir/StructureDefinition/data-absent-reason"); Assert.IsNotNull(extDefn); Assert.IsInstanceOfType(extDefn, typeof(StructureDefinition)); try { extDefn = source.GetExtensionDefinition("http://hl7.org/fhir/StructureDefinition/Patient"); Assert.Fail(); } catch { ; } }