God knows all that because God is only a Mystery to us, not to Himself. God alone knows God.
“No one else besides Thee hath, at any time, been able to fathom Thy mystery, or befittingly to extol Thy greatness. Unsearchable and high above the praise of men wilt Thou remain for ever.” Gleanings, p.5
No, God is not evolved and God is not a creature. Humans evolved and we are intelligent and emotional because we were made and evolved in the image of God.
You are correct, no test will do that, but with enough effort and research, "potentially" we can determine that for ourselves. Not everyone will be successful.
God definitely is external to the self, and God can be found in nature because God is reflected in nature and in everything in existence.
“Whatever is in the heavens and whatever is on the earth is a direct evidence of the revelation within it of the attributes and names of God, inasmuch as within every atom are enshrined the signs that bear eloquent testimony to the revelation of that Most Great Light.....
…From that which hath been said it becometh evident that all things, in their inmost reality, testify to the revelation of the names and attributes of God within them. Each according to its capacity, indicateth, and is expressive of, the knowledge of God. So potent and universal is this revelation, that it hath encompassed all things visible and invisible....”
Man, the noblest and most perfect of all created things, excelleth them all in the intensity of this revelation, and is a fuller expression of its glory.And of all men, the most accomplished, the most distinguished, and the most excellent are the Manifestations of the Sun of Truth. Nay, all else besides these Manifestations, live by the operation of Their Will, and move and have their being through the outpourings of Their grace.” Gleanings From the Writings of Bahá’u’lláh, pp. 177-179