Even as (kathōs). In proportion as (1Th 1:5) and so inasmuch as (Phi 1:7; Eph 1:4).
The testimony of Christ (to marturion tou Christou). Objective genitive, the testimony to or concerning Christ, the witness of Paul’s preaching.
Was confirmed in you (ebebaiōthē en humin). First aorist passive of bebaioō, old verb from bebaios and that from bainō, to make to stand, to make stable. These special gifts of the Holy Spirit which they had so lavishly received (ch. 1 Corinthians 12) were for that very purpose.