fix: add checks and handle errors brew-bump.sh

feat(script): add steps-lib, is_env_var_set & test

feat(brew-bump): add check for VERSION

feat(brew-bump): check HOMEBREW_GITHUB_API_TOKEN

feat(steps-lib): add directory_exists helper fn

fix(brew-bump): check that git clone worked

feat(brew-bump): add check for remote upstream

fix: remove upstream command thing

feat(steps-lib): add file_exists helper function

feat(brew-bump): add check for git-askpass.sh

feat(steps-lib): add is_executable function & test

feat(brew-bump): add check for is_executable

refactor: use GIT_ASKPASS as variable

ci/steps/steps-lib.sh

@@ -0,0 +1,47 @@
+#!/usr/bin/env bash
+
+# This is a library which contains functions used inside ci/steps
+#
+# We separated it into it's own file so that we could easily unit test
+# these functions and helpers
+
+# Checks whether and environment variable is set.
+# Source: https://stackoverflow.com/a/62210688/3015595
+is_env_var_set() {
+  local name="${1:-}"
+  if test -n "${!name:-}"; then
+    echo 0
+  else
+    echo 1
+  fi
+}
+
+# Checks whether a directory exists.
+directory_exists() {
+  local dir="${1:-}"
+  if [[ -d "${dir:-}" ]]; then
+    echo 0
+  else
+    echo 1
+  fi
+}
+
+# Checks whether a file exists.
+file_exists() {
+  local file="${1:-}"
+  if test -f "${file:-}"; then
+    echo 0
+  else
+    echo 1
+  fi
+}
+
+# Checks whether a file is executable.
+is_executable() {
+  local file="${1:-}"
+  if [ -f "${file}" ] && [ -r "${file}" ] && [ -x "${file}" ]; then
+    echo 0
+  else
+    echo 1
+  fi
+}