Update package_manager_exists.sh

Author: CLHatch

.scripts/package_manager_exists.sh

@@ -13,5 +13,24 @@ package_manager_exists() {
 }
 
 test_package_manager_exists() {
-    warn "CI does not test package_manager_exists."
+    local ForcePass='' # Force the tests to pass even on failure if set to a non-empty value
+    local -i result=0
+    local -a Test=(
+        apt YES
+        Apt YES
+        nala NO
+        Nala NO
+        brew NO
+        xxx NO
+    )
+    run_unit_tests_pipe "App" "App" "${ForcePass}" < <(
+        for ((i = 0; i < ${#Test[@]}; i += 2)); do
+            printf '%s\n' \
+                "${Test[i]}" \
+                "${Test[i + 1]}" \
+                "$(run_script 'package_manager_is_installed' "${Test[i]}" && echo "YES" || echo "NO")"
+        done
+    )
+    result=$?
+    return ${result}
 }