Augustine of Hippo — as excerpted in the Catena Aurea on John 6:1-14

“(de verb. Dom. Serm. 17) One kind of temptation leads to sin, with which God never tempts any one; (James 1:13.) and there is another kind by which faith is tried. (Deut. 13:3.) In this sense it is said that Christ proved His disciple. This is not meant to imply that He did not know what Philip would say; but is an accommodation to men’s way of speaking. For as the expression, Who searcheth the hearts of men, does not mean the searching of ignorance, but of absolute knowledge; so here, when it is said that our Lord proved Philip, we must understand that He knew him perfectly, but that He tried him, in order to confirm his faith. The Evangelist himself guards against the mistake which this imperfect mode of speaking might occasion, by adding, For He Himself knew what He would do.”