dataSet <- read.csv("creditcard_german.csv", header=FALSE)
# ... split into trainSet and testSet ...

trainSet[] <- lapply(trainSet, as.factor)
testSet[] <- lapply(testSet, as.factor)

# V25 is the class variable
bn = naive.bayes(trainSet, training = "V25")
fitted = bn.fit(bn, trainSet, method = "bayes")
pred = predict(fitted , testSet)

...