Run script/test quietly with coverage, rerun failed tests verbosely (closes #315)

The first run is go test -race -cover without -v, so a green run prints
one line per package with its coverage. On failure, the top-level tests
named on "--- FAIL:" lines are rerun with -v in the packages that failed,
then the script exits 1 whatever the rerun's result. Rerunning only the
failed tests keeps a red build log far below the 2 MiB at which the
Docker build cuts it off (issue 414). The timeout, -p 4 -parallel 8 and
their header comment are unchanged.

Model: opus-5-5

script/test

@@ -28,10 +28,12 @@
 # -race every test binary and every link costs a few hundred MB, so the
 # defaults (one per core) add up to several GB on a many-core host.
 #
-# No -v: the Docker build cuts each step's log off at 2 MiB, and verbose output
-# from the whole suite passes that before a failure is printed. Without it, go
-# test prints one result line per package and, for a package that fails,
-# everything its tests wrote, application log lines included.
+# The first run has no -v: go test then prints one result line per package,
+# with its coverage, and for a package that fails, everything its tests wrote,
+# application log lines included. Verbose output from the whole suite passes
+# the 2 MiB at which the Docker build cuts off each step's log, so on a failure
+# only the tests that failed run again, with -v. The script exits 1 after that
+# rerun whatever its result: the first run already showed the suite is broken.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
@@ -39,7 +41,34 @@ ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 main() {
     cd "$ROOT"
     "$ROOT/script/assets"
-    go test -race -p 4 -parallel 8 -timeout 90s ./...
+
+    log="$(mktemp -t webhooker-test.XXXXXXXX)"
+    rcfile="$(mktemp -t webhooker-test-rc.XXXXXXXX)"
+    trap 'rm -f "$log" "$rcfile"' EXIT INT TERM
+
+    # The pipeline's status is tee's, and POSIX sh has no pipefail, so go
+    # test's status travels via a file. Output still streams live.
+    {
+        go test -race -cover -p 4 -parallel 8 -timeout 90s ./... 2>&1 \
+            && echo 0 >"$rcfile" || echo $? >"$rcfile"
+    } | tee "$log"
+    if [ "$(cat "$rcfile")" -eq 0 ]; then
+        return
+    fi
+
+    # go test reports a failed test as a line starting "--- FAIL: TestName"
+    # (a failed subtest's line is indented, and reruns with its parent), and
+    # a failed package as "FAIL<tab>package/path<tab>...". A failure that
+    # names no test, such as a build error or a timeout, is already shown in
+    # full above, so there is nothing to rerun.
+    tests="$(awk '/^--- FAIL: / { print $3 }' "$log" | paste -s -d '|' -)"
+    packages="$(awk '/^FAIL\t/ { print $2 }' "$log")"
+    if [ -n "$tests" ]; then
+        echo "--- Rerunning the failed tests with -v for details ---"
+        go test -race -v -p 4 -parallel 8 -timeout 90s \
+            -run "^($tests)\$" $packages || true
+    fi
+    exit 1
 }
 
 main "$@"