I've tried to google it but can't find an answer. How did a woman become an oracle? Was she raised for the purpose? Was there some sort of test to check for a divine connection? Were Oracles forced to be oracles?
The women did not speak coherently. The "priests" interpreted what the women said. Delphi had gas seeping from a crevice until an earthquake shut off the gas. The Oracle was wealthy and was looted a time or two.
The Delphians, or more properly speaking the noble families of Delphi, had the superintendence of the oracle. Among the Delphian aristocracy, however, there were five families which traced their origin to Deucalion, and from each of these one of the five priests, called ὅσιοι, was taken (Eurip. Ion, 411; Plut. Quaest. Gr. c9). Three of the names of these families only are known, viz. the Cleomantids, the Thracids (Diod. XVI.24; Lycurg. c. Leocrat. p158), and the Laphriads (Hesych. s.v.).
The ὅσιοι, together with the high priest or prophetes, held their offices for life, and had the control of all the affairs of the sanctuary and of the sacrifices (Herod. VIII.136). That these noble families had an immense influence upon the oracle is manifest from numerous instances, and it is not improbable that they were its very soul, and that it was they who dictated the pretended revelations of the god (see especially, Lycurg. c. Leocrat. p158; Herod. VII.141, VI.66; Plut. Pericl. 21; Eurip. Ion, 1219, 1222, 1110).
The Delphic oracle had at all times a leaning in favour of the Greeks of the Doric race; but the time when it began to lose its influence must be dated from the period when Athens and Sparta entered upon their struggle for the supremacy in Greece; for at this time the partiality for Sparta became so manifest, that the Athenians and their party began to lose all reverence and esteem for it (Plut. Demosth. 20), and the oracle became a mere instrument in the hands of a political party. In the times of Cicero and Plutarch many believed that the oracle had lost the powers which it had possessed in former days; but it still continued to be consulted down to the times of the emperor Julian, until at last it was entirely done away with by Theodosius.
As an aside, I thoroughly recommend visiting Delphi. I found it almost tourist free and so much more impressive than the over-rated, tourist swarmed, Acropolis in Athens.
BTW the gas inhaile dby the Pytho was Ethane which brings on euphoria and mild asphyxia but is recoverable.
The Complex is built right up the mountain the amphitreatre and gymnasia at the bottom, the temples of the Oracle, then the large niches in the rock where each City State of Greece would store it relics and precious items before going to War and almost at the top of the mountain - a running track. Views are breathtaking and the (small) museum much better than the empty nothing of glass and steel in Athens - a gem!.