# `Bylaw.Credo.Check.Testing.NoGlobalStateInTests`
[🔗](https://github.com/ryanzidago/bylaw/blob/v0.1.0-alpha.1/lib/bylaw/credo/check/testing/no_global_state_in_tests.ex#L1)

## Basics

> #### This check is disabled by default. {: .neutral}
>
> [Learn how to enable it](`e:credo:config_file.html#checks`) via `.credo.exs`.

This check has a base priority of `higher` and works with any version of Elixir.

## Explanation

Avoid reading or mutating global application and system environment state
from tests.

## Examples

Avoid:

      test "uses config" do
        Application.put_env(:my_app, :feature_enabled?, true)
        assert Feature.enabled?()
      end

Prefer:

      test "uses config" do
        assert Feature.enabled?(%{feature_enabled?: true})
      end

## Notes

Application and system environment are shared process-wide state. Tests
that read or mutate that state can race with each other when the suite
runs concurrently, especially when a test forgets to restore a value.

Prefer passing dependencies or configuration explicitly. If a test needs
a substitute implementation, use a behaviour-backed module or mock that
is scoped to the test process.

Path exclusions are matched against the source filename and are intended for generated files or temporary migration areas.

The check uses static AST analysis, so dynamic code generation and macro-expanded code may fall outside its signal.

## Options

Configure options in `.credo.exs` with the check tuple:

```elixir
%{
  configs: [
    %{
      name: "default",
      checks: [
        {Bylaw.Credo.Check.Testing.NoGlobalStateInTests,
         [
           excluded_paths: ["test/support/"]
         ]}
      ]
    }
  ]
}
```

- `:excluded_paths` - Paths containing any configured string are skipped. Use this for test support files that intentionally own global test configuration.

## Usage

Add this check to Credo's `checks:` list in `.credo.exs`:

```elixir
%{
  configs: [
    %{
      name: "default",
      checks: [
        {Bylaw.Credo.Check.Testing.NoGlobalStateInTests, []}
      ]
    }
  ]
}
```

## Check-Specific Parameters

Use the following parameters to configure this check:

### `:excluded_paths`

  Paths containing any configured string are skipped. Use this for test
  support files that intentionally own global test configuration.
  

*This parameter defaults to* `[]`.

## General Parameters

Like with all checks, [general params](`e:credo:check_params.html`) can be applied.

Parameters can be configured via the [`.credo.exs` config file](`e:credo:config_file.html`).

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*Consult [api-reference.md](api-reference.md) for complete listing*