Use the Transcendental Values which make up The Good: namely, truth, beauty and virtue.
What we are looking for is planned, strategic violation of the transcendental Goods.
Of course, since we are all sinners, we all violate these Goods repeatedly, and cannot help ourselves. But such inevitable violations ought to be forced, coerced, unthinking, tactical, short-termist, impulsive.
However, the enemy violates the Good with care, attention and much labour.
These violations are gratuitous.
Dishonesty - when it is deliberate, is perhaps the best and clearest hallmark of the enemy and his servants.
For example - yesterday I stumbled across a website for an organization which calls itself 'Affinity' and used to be the British Evangelical Council, and was closely associated with the late great Martyn Lloyd Jones. Presumably this organization used to be a powerful force for real Christianity.
But now... a swift perusal of the Mission Statement and the use of language
reveals that this organization is now deliberately dishonest, hence anti-Christian, hence the enemy.
The destruction of beauty is another test.
Organizations which go to a great deal of trouble and expense to erect objectively ugly buildings or install such works of art, are evil.
I am not talking about Kitsch - which is sincere but incompetent attempts to create beauty; I am not talking about accidental ugliness due to the need for haste, cheapness or convenience - I am talking about the kind of expensive, dysfunctional, aggressively-ugly modern architucture which is normal at present.
This is capped and clinched by denial of the ugliness of what has been created - and the attempt to pass it off as beautiful; to argue its beauty ('award winning'), to boast of its beauty...
Aggressive promotion of sin is another test - perhaps the most obvious one.
When a person or oganization decides to take something which is regarded as a sin throughout the Christian world and/or human history and by the consensus of Mankind; and chooses to invert this evaluation and thereby not just deny but actively propagandize for sin; and in a planned, strategic, deliberate fashion...
well, all this is very obviously the enemy at work.
It doesn't make any difference if such a person imagines they are Christian, or if this is done by an organization which imagines it is a Christian church.
Those who attack the Good, those who invert evil and call it good: they are the enemy - and this is how we know them.
Not by their self-image, not by their names or labels, not by their exposition of supposed Good motivations.
All that stuff must be ignored.
Don't listen to what they say, look at what they do - and what they do in a planned, strategic, deliberate, care-full way.