misk-policy-testing

This module provides a simple abstraction for mocking policy engine requests in unit tests. Additionally, this module allows developers to run Open Policy Agent (OPA) instances locally during development, fully integrated into the container lifecycle. This feature uses docker to launch the latest OPA image, mounting a local policy directory and configuring the service to use the local instance for queries.

Usage

For mocking functionality in unit tests, use FakeOpaModule:

install(FakeOpaModule())

For an improved local development experience, use the OpaDevelopmentModule. This module should be used alongside the OpaModule in the misk-policy package.

install(OpaDevelopmentModule())
//or
install(OpaDevelopmentModule(policyDirectory = "some path", withLogging = true, preferredImageVersion = "0.40.0"))

The default policy directory is service/src/policy and the recommended location to keep policies accessible for local testing.

Unit testing

The testing framework make the FakeOpaPolicyEngine interface available as an implementation of OpaPolicyEngine. The fake functions more like a mock and similar to misk-feature-testing. Developers should use the fake interface, to add specific return values for given document names and inputs.

@MiskTest(startService = false)
internal class FakeOpaPolicyEngineTest {
  @MiskTestModule val module = FakeOpaModule()

  @Inject lateinit var fakeOpaPolicyEngine: FakeOpaPolicyEngine
  @Inject lateinit var opaPolicyEngine: OpaPolicyEngine

  @Test
  fun `Override document without input`() {
    fakeOpaPolicyEngine.addOverride("test", TestResponse("value"))
    val evaluate = opaPolicyEngine.evaluate<TestResponse>("test")
    assertThat(evaluate).isEqualTo(TestResponse("value"))
  }

  @Test
  fun `Override document with input`() {
    fakeOpaPolicyEngine.addOverrideForInput("test", TestRequest("key"), TestResponse("value"))
    val evaluate = opaPolicyEngine.evaluate<TestRequest, TestResponse>("test", TestRequest("key"))
    assertThat(evaluate).isEqualTo(TestResponse("value"))
  }

  data class TestRequest(
    val something: String
  ) : OpaRequest()

  data class TestResponse(
    val something: String
  ) : OpaResponse()

Local development

It is possible spin up a docker image of OPA, with all the local policy loaded as part of misk's lifecycle. This allows developers to run an actual instance of the policy engine, providing end-to-end testing capability during development. To use this feature, setup OpaDevelopmentModule. That's it!

install(OpaDevelopmentModule())
//or
install(OpaDevelopmentModule(policyDirectory = "some path", withLogging = true))

Once installed, misk will automatically instantiate a docker container, mounting the policyDirectory (default: service/src/policy) into it and running opa run -s -b -w /policies , where the policies directory is the mapped directory. while the service is running, OPA is queryable on port 8181 locally. See LocalOpaService.kt for more information and ways to change this behavior.