Obtest \ob-TEST\ , verb;
1. To supplicate earnestly; beseech
2. To invoke as witness
3. To protest
4. To make supplication; beseech
I've written several times about folk (a.k.a. false) etymologies. Sometimes they are just silly (like fuck being an acronym of "for unlawful carnal knowledge") and others are honest mistakes (like believing male and female are related words). Obtest is not exactly a common word, but it does show us just how easy it is to make erroneous assumptions.
At first glance this word looks like a superlative: obt-est, the most ob(t). So what does obt or ob mean? I don't know, but there are a few hundred thousand English words.
Turns out, obtest is a verb taken from Latin obtestari ("to beseech, implore, to call to witness, to affirm solemnly, to protest"), which is based on testari ("testate, bear witness, testify") with ob- being a prefix meaning "toward, in the direction of."
By the way, there is a word ob in English that is not a shortening of some other word. It means "a wizard or magician; a sorcerer" and was borrowed from Hebrew in the mid-17th century.