Initialize a test counter, a matrix used to tally tests, their stack depth
and the execution order as the trace associated with key
is hit. Each
test trace is an environment, which allows assignment into a pre-allocated
tests
matrix with minimall reallocation.
new_test_counter(key)
generated with key()
The tests
matrix has columns tests
, depth
and i
,
corresponding to the test index (the index of the associated test in
.counters$tests
), the stack depth when the trace is evaluated and the
number of traces that have been hit so far during test evaluation.