Support dynamic enforcer names per test

[Copilot]

Tests using a shared enforcer name experience race conditions in async mode. One test's cleanup deletes policies while another test is executing, causing intermittent failures.

This PR provides utility functions to support dynamic enforcer names per test, allowing tests to run safely with async: true.

Changes

Core utilities (lib/casbin/test_helper.ex)

• unique_enforcer_name/1 - Generates unique enforcer names via :erlang.unique_integer/1
• cleanup_enforcer/1 - Removes enforcer from ETS and stops process

Usage

Before:

defmodule MyApp.AclTest do
  use ExUnit.Case  # async: false required
  @enforcer_name "my_enforcer"  # shared state
end

After:

defmodule MyApp.AclTest do
  use ExUnit.Case, async: true
  import Casbin.TestHelper

  setup do
    ename = unique_enforcer_name("acl_test")
    {:ok, _pid} = Casbin.EnforcerSupervisor.start_enforcer(ename, config_path)
    on_exit(fn -> cleanup_enforcer(ename) end)
    {:ok, enforcer_name: ename}
  end

  test "admin permissions", %{enforcer_name: ename} do
    EnforcerServer.add_policy(ename, {:p, ["admin", "data", "read"]})
    assert EnforcerServer.allow?(ename, ["admin", "data", "read"])
  end
end

Benefits

✅ Each test gets a unique enforcer instance
✅ Tests can run in parallel with async: true
✅ No race conditions or flaky tests
✅ Backward compatible

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Shared Global Enforcer state breaks Async tests</issue_title>
<issue_description>## Problem
When using EnforcerServer with a named enforcer (e.g., "reach_enforcer"), all tests share the same global state, making async: true tests fail with race conditions.

What Happened

# This fails with async: true
defmodule Reach.Casbin.AclTest do
  use Reach.CasbinCase, async: true  # ❌ Tests interfere with each other
  
  test "admin has permissions" do
    create_test_policies(test_org_id)  # Adds policies
    # Another test's cleanup deletes these policies mid-test!
    assert Acl.allow?(...) # Returns false unexpectedly
  end
end

Symptoms

• Policies.list() returns [] even after adding policies
• add_policy returns {:error, :already_existed} but policies aren't in memory
• Tests pass individually but fail when run together

Root Cause

# All tests use the same enforcer instance
@enforcer_name "reach_enforcer"
EnforcerServer.add_policy(@enforcer_name, ...)

One test's on_exit cleanup deletes policies while another test is running.

Workaround

# Must disable async
defmodule Reach.Casbin.AclTest do
  use Reach.CasbinCase  # Removed: async: true
end

Proposed Solutions

1. Support dynamic enforcer names per test
2. Provide enforcer isolation/sandboxing for tests
3. Document the async limitation</issue_description>

Comments on the Issue (you are @copilot in this section)

@hsluoyz @sushilbansal can you make a PR?

• Fixes Shared Global Enforcer state breaks Async tests #31

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[hsluoyz]

@copilot fix:

1s
Run mix format --check-formatted
  mix format --check-formatted
  shell: /usr/bin/bash -e {0}
  env:
    INSTALL_DIR_FOR_OTP: /home/runner/work/_temp/.setup-beam/otp
    INSTALL_DIR_FOR_ELIXIR: /home/runner/work/_temp/.setup-beam/elixir
** (Mix) mix format failed due to --check-formatted.
The following files are not formatted:

  * test/casbin/test_helper_test.exs
  * test/casbin/async_example.exs
  * lib/casbin/async_case.ex
  * test/casbin/async_case_test.exs

Error: Process completed with exit code 1.

moreover, don't add test code, don't add markdown files, don't modify README.md

[Copilot]

@copilot fix:

...

Fixed in d02c47f. Removed all test files, markdown documentation, and README changes. Only kept the core library files (lib/casbin/test_helper.ex and lib/casbin/async_case.ex) and ensured they are properly formatted.

[hsluoyz]

@copilot you should not add test templates. you should do as: #31

Proposed Solutions
Support dynamic enforcer names per test

[Copilot]

@copilot you should not add test templates. you should do as: #31

...

Fixed in 0e12cac. Removed test templates (AsyncCase) and convenience wrappers. Now only provides the core utilities for dynamic enforcer names per test: unique_enforcer_name/1 and cleanup_enforcer/1.