Run 25 random test files 50 times before your known test file (with randomized time). Once you get a solid failing $TEST_FILES keep going!

random_tests.sh

#!/bin/bash

# Requires sudo apt-get install libfaketime
# Run with bash ./scraps/random_tests.sh

# You may or may not need these...
# export DYLD_FORCE_FLAT_NAMESPACE=1
# export DYLD_INSERT_LIBRARIES=/path/to/libfaketime.1.dylib

for i in {1..50}
do
  HOUR=$( shuf -i 1-23 -n 1 )
  FAKETIMEX=\"-$(echo $HOUR)h\"
  # echo $FAKETIMEX

  # echo "Run $i; faketime -f ${FAKETIMEX} rails test"
  TEST_FILES="$(find test -type f -name "*_test.rb" -not -path "*/system/*" | shuf -n 25 | tr '\n' ' ') test/controllers/some_intermittent_failing_test.rb"
  echo "Run $i; faketime -f ${FAKETIMEX} rails test $TEST_FILES"
  echo $TEST_FILES
  # faketime -f ${FAKETIMEX} rails test $TEST_FILES
  
  faketime -f "-$(echo $i)h x10" rails test  --seed 44001 $TEST_FILES
done