The output of $test changes whether or not the bash grouping is piped into another command or not.

test.sh

#!/bin/bash
set -e -o pipefail

test=1
{ echo "test"; echo "test2" && test=0; } | cat > /dev/null
echo "$test"

test=1
{ echo "test"; echo "test2" && test=0; } > /dev/null
echo "$test"

# $ ./test.sh
# 1
# 0