Configuration

Gremlins can be configured via (in order of precedence):

1. command flags
2. environment variables
3. configuration files

Command flags

Flags have the higher priority and override all the other means of setting behaviours. Please refer to the specific command documentation to learn how to use them.

Configuration files

Gremlins can be configured with a configuration file.

Location

The configuration file can be placed in (in order of precedence)

1. ./.gremlins.yaml (the current directory)
2. /etc/gremlins/gremlins.yaml
3. $XDG_CONFIG_HOME/gremlins/gremlins.yaml
4. $HOME/.gremlins.yaml

Hint

XDG_CONFIG_HOME is usually ~/.config.

Override

The config file can be overridden with the --config flag.

gremlins unleash --config=myConfig.yaml

Reference

Here is a complete configuration file with all the properties set to their defaults:

silent: false
unleash:
  dry-run: false
  tags: ""
  output: ""
  threshold: #(1)
    efficacy: 0
    mutant-coverage: 0

mutants:
  arithmetic-base:
    enabled: true
  conditionals-boundary:
    enabled: true
  conditionals-negation:
    enabled: true
  increment-decrement:
    enabled: true
  invert-negatives:
    enabled: true

1. Thresholds are set by default to 0, which means they are not enforced. For further information check the specific documentation.

Tip

You can validate the configuration file using the provided JSON Schema (ex. using it in your editor). The schema can be found at https://gremlins.dev/0.2/schema/configuration.json.

Environment variables

Gremlins can be configured via environment variables as well. You can construct the variable name referring to the configuration file format. They start with GREMLINS_, and each dot and dash becomes an underscore.

For example:

mutants:
  arithmetic-base:
    enabled: true

Can be set with:

export GREMLINS_MUTANTS_ARITHMETIC_BASE=true