testing: reduce memory used by subtest names
This is heavily based on CL 341336 by Joe Tsai and CL 351452 by
Jay Conrod.
T.Run and T.Name use a map[string]int64 to hold the next suffix to use
when duplicate names are passed to T.Run. This map necessarily retains
one entry per unique name. However, it's a waste of memory to retain
one entry per duplicate name: when we encounter the Nth duplicate, we
know that names 00 through N-1 have been used just by looking at N.
We do still need to store (and check for collisions againsts) explicit
names provided by the caller. For example, if the user passes in "a",
then "a#01", then "a" again, we cannot deduplicate the second "a" to
"a#01" — we need to instead skip ahead to "a#02". We can do so by
checking the count of "a", then generating a proposed deduplicated
name, then double-checking that proposed name against only the
explicit names so far.
This somewhat reduces memory usage for tests that spawn large numbers
of duplicate subtests, but doesn't solve the problem of memory growth
for fuzzing — we still have to track all of the explicit,
user-provided subtest names, and in a long-running fuzz test that set
alone may be unbounded.
This fixes memory growth for the example described in
https://golang.org/issue/44517#issuecomment-
897104060,
but not the one in
https://golang.org/issue/44517#issuecomment-
933825661.
For #44517
Change-Id: Ia159ecfcf44561ba67508d3af6377c27856df31d
Reviewed-on: https://go-review.googlesource.com/c/go/+/354749
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Emmanuel Odeke <emmanuel@orijtech.com>
Reviewed-by: Jay Conrod <jayconrod@google.com>