Avoid empty --features= arg to avoid unnecessary cargo building

ci/integration-tests.sh

@@ -3,7 +3,11 @@
 # Runs all integration tests in the tree serially
 #
 set -e
-FEATURES="$1"
+maybeFeatures=
+if [[ -n $1 ]]; then
+  maybeFeatures="--features=$1"
+fi
+
 cd "$(dirname "$0")/.."
 source ci/_
 export RUST_BACKTRACE=1
@@ -14,7 +18,8 @@ for test in {,*/}tests/*.rs; do
   test=${test%.rs} # basename x .rs
   (
     export RUST_LOG="$test"=trace,$RUST_LOG
-    _ cargo test --all --verbose --features="$FEATURES" --test="$test" \
+    # shellcheck disable=SC2086 # Don't want to double quote $maybeFeatures
+    _ cargo test --all --verbose $maybeFeatures --test="$test" \
       -- --test-threads=1 --nocapture
   )
 done