One of the biggest issues in magic is the threat of self-delusion, or delusion by exterior forces (spirits, etc.), making testing a vital requirement. This is emphasised time and time again in Golden Dawn material, with a variety of methods given.
I devoted a chapter to this in my recently published book Enochian Magic in Practice, including a slew of techniques, from challenges Dee himself used, to the "utility belt" of tests that Mathers and Westcott supplied.
For now, however, I want to look at how the 5=6 Ceremony guides us on this matter. If we look at the Obligation taken by an Adeptus Minor, the tenth clause, relating to Malkuth, states the following:
"Finally, if in my travels, I should meet a stranger who professes to be a member of the Rosicrucian Order, I will examine him with care before acknowledging him to be so."
This is sound advice on a mundane level, but it also (like all clauses of the Obligation) has a magical application: that, if in our occult travels, we should meet a strange spirit that professes to be anything or anyone, but most especially if it professes to be a major spirit like an archangel (who may be considered members of the Rosicrucian Order), that we will examine (test) it before acknowledging it to be so.
The Virtue of Malkuth is Discrimination or Discernment, and it is a vital skill to learn from the outset, especially when engaging in practical occult work. It is very easy to get lost in a sea of images, especially further up the Tree of Life, which is why this Virtue is placed at the threshold of our path, that we might make a true journey.