Testimonies have played a prominent role in Congregationalism, historically. Along with some other Churches, they are "trademark Congregational". In my own ministr(ies), testimonies have been prominent. There is some method behind this, though. In the case of conversion especially, which is the most important testimony, I generally have three rules of thumb:
• Let the person share it first in a Church group, then with the Church.OBSERVATION: At the time of the founding of the Congregational Church, every member, without exception, would give their testimony.
• Look first for abiding fruit. One may argue that a person should make immediate public confession and be baptised. In my experience, there have been too many people who did that, but did not prove themselves thereafter. In my own situation, some have faked conversion where they thought they would derive some benefit from it.
• Plan public testimonies, rather than putting people up impromptu. I think this guarantees the quality of a testimony, and widens the "pool" of testimonies where impromptu testimonies may favour a certain kind of personality.