unit-testing - 如何在 Kotlin 中管理单元测试资源，例如启动/停止数据库连接或嵌入式 Elasticsearch 服务器？

Question

在我的 Kotlin JUnit 测试中，我想启动/停止嵌入式服务器并在我的测试中使用它们。

我尝试在我的测试类中的方法上使用 JUnit @Before 注释，它工作正常，但这不是正确的行为，因为它运行每个测试用例而不是只运行一次。

因此，我想在方法上使用 @BeforeClass 注释，但是将其添加到方法会导致错误，指出它必须在静态方法上。 Kotlin 似乎没有静态方法。这同样适用于静态变量，因为我需要保留对嵌入式服务器的引用以供测试用例使用。

那么如何为我的所有测试用例只创建一次这个嵌入式数据库？

class MyTest {
    @Before fun setup() {
       // works in that it opens the database connection, but is wrong 
       // since this is per test case instead of being shared for all
    }

    @BeforeClass fun setupClass() {
       // what I want to do instead, but results in error because 
       // this isn't a static method, and static keyword doesn't exist
    }

    var referenceToServer: ServerType // wrong because is not static either

    ...
}

注意: 这个问题是作者有意编写和回答的 (Self-Answered Questions)，因此常见的 Kotlin 主题的答案出现在 SO 中。

Answer 1

您的单元测试类通常需要一些东西来管理一组测试方法的共享资源。在 Kotlin 中，您可以不在测试类中使用 @BeforeClass 和 @AfterClass，而是在其 companion object 中使用连同 @JvmStatic annotation .

测试类的结构如下:

class MyTestClass {
    companion object {
        init {
           // things that may need to be setup before companion class member variables are instantiated
        }

        // variables you initialize for the class just once:
        val someClassVar = initializer() 

        // variables you initialize for the class later in the @BeforeClass method:
        lateinit var someClassLateVar: SomeResource 
  
        @BeforeClass @JvmStatic fun setup() {
           // things to execute once and keep around for the class
        }

        @AfterClass @JvmStatic fun teardown() {
           // clean up after this class, leave nothing dirty behind
        }
    }

    // variables you initialize per instance of the test class:
    val someInstanceVar = initializer() 

    // variables you initialize per test case later in your @Before methods:
    var lateinit someInstanceLateZVar: MyType 

    @Before fun prepareTest() { 
        // things to do before each test
    }

    @After fun cleanupTest() {
        // things to do after each test
    }

    @Test fun testSomething() {
        // an actual test case
    }

    @Test fun testSomethingElse() {
        // another test case
    }

    // ...more test cases
}  

鉴于以上内容，您应该阅读以下内容:

• companion objects - 类似于 Java 中的 Class 对象，但每个类都有一个非静态的单例
• @JvmStatic - 将伴随对象方法转换为 Java 互操作外部类上的静态方法的注释
• lateinit - 当您有一个明确定义的生命周期时，允许稍后初始化 var 属性
• Delegates.notNull() - 可以代替 lateinit 用于在读取前应至少设置一次的属性。

以下是管理嵌入式资源的 Kotlin 测试类的更完整示例。

第一个是从Solr-Undertow tests复制和修改的，在运行测试用例之前，配置并启动 Solr-Undertow 服务器。测试运行后，它会清除测试创建的所有临时文件。它还确保在运行测试之前环境变量和系统属性是正确的。在测试用例之间，它会卸载任何临时加载的 Solr 内核。测试:

class TestServerWithPlugin {
    companion object {
        val workingDir = Paths.get("test-data/solr-standalone").toAbsolutePath()
        val coreWithPluginDir = workingDir.resolve("plugin-test/collection1")

        lateinit var server: Server

        @BeforeClass @JvmStatic fun setup() {
            assertTrue(coreWithPluginDir.exists(), "test core w/plugin does not exist $coreWithPluginDir")

            // make sure no system properties are set that could interfere with test
            resetEnvProxy()
            cleanSysProps()
            routeJbossLoggingToSlf4j()
            cleanFiles()

            val config = mapOf(...) 
            val configLoader = ServerConfigFromOverridesAndReference(workingDir, config) verifiedBy { loader ->
                ...
            }

            assertNotNull(System.getProperty("solr.solr.home"))

            server = Server(configLoader)
            val (serverStarted, message) = server.run()
            if (!serverStarted) {
                fail("Server not started: '$message'")
            }
        }

        @AfterClass @JvmStatic fun teardown() {
            server.shutdown()
            cleanFiles()
            resetEnvProxy()
            cleanSysProps()
        }

        private fun cleanSysProps() { ... }

        private fun cleanFiles() {
            // don't leave any test files behind
            coreWithPluginDir.resolve("data").deleteRecursively()
            Files.deleteIfExists(coreWithPluginDir.resolve("core.properties"))
            Files.deleteIfExists(coreWithPluginDir.resolve("core.properties.unloaded"))
        }
    }

    val adminClient: SolrClient = HttpSolrClient("http://localhost:8983/solr/")

    @Before fun prepareTest() {
        // anything before each test?
    }

    @After fun cleanupTest() {
        // make sure test cores do not bleed over between test cases
        unloadCoreIfExists("tempCollection1")
        unloadCoreIfExists("tempCollection2")
        unloadCoreIfExists("tempCollection3")
    }

    private fun unloadCoreIfExists(name: String) { ... }

    @Test
    fun testServerLoadsPlugin() {
        println("Loading core 'withplugin' from dir ${coreWithPluginDir.toString()}")
        val response = CoreAdminRequest.createCore("tempCollection1", coreWithPluginDir.toString(), adminClient)
        assertEquals(0, response.status)
    }

    // ... other test cases
}

另一个作为嵌入式数据库的本地 AWS DynamoDB 启动(从 Running AWS DynamoDB-local embedded 复制并稍作修改)。此测试必须在其他任何事情发生之前破解 java.library.path，否则本地 DynamoDB(使用带有二进制库的 sqlite)将无法运行。然后它启动一个服务器来共享所有测试类，并清理测试之间的临时数据。测试:

class TestAccountManager {
    companion object {
        init {
            // we need to control the "java.library.path" or sqlite cannot find its libraries
            val dynLibPath = File("./src/test/dynlib/").absoluteFile
            System.setProperty("java.library.path", dynLibPath.toString());

            // TEST HACK: if we kill this value in the System classloader, it will be
            // recreated on next access allowing java.library.path to be reset
            val fieldSysPath = ClassLoader::class.java.getDeclaredField("sys_paths")
            fieldSysPath.setAccessible(true)
            fieldSysPath.set(null, null)

            // ensure logging always goes through Slf4j
            System.setProperty("org.eclipse.jetty.util.log.class", "org.eclipse.jetty.util.log.Slf4jLog")
        }

        private val localDbPort = 19444

        private lateinit var localDb: DynamoDBProxyServer
        private lateinit var dbClient: AmazonDynamoDBClient
        private lateinit var dynamo: DynamoDB

        @BeforeClass @JvmStatic fun setup() {
            // do not use ServerRunner, it is evil and doesn't set the port correctly, also
            // it resets logging to be off.
            localDb = DynamoDBProxyServer(localDbPort, LocalDynamoDBServerHandler(
                    LocalDynamoDBRequestHandler(0, true, null, true, true), null)
            )
            localDb.start()

            // fake credentials are required even though ignored
            val auth = BasicAWSCredentials("fakeKey", "fakeSecret")
            dbClient = AmazonDynamoDBClient(auth) initializedWith {
                signerRegionOverride = "us-east-1"
                setEndpoint("http://localhost:$localDbPort")
            }
            dynamo = DynamoDB(dbClient)

            // create the tables once
            AccountManagerSchema.createTables(dbClient)

            // for debugging reference
            dynamo.listTables().forEach { table ->
                println(table.tableName)
            }
        }

        @AfterClass @JvmStatic fun teardown() {
            dbClient.shutdown()
            localDb.stop()
        }
    }

    val jsonMapper = jacksonObjectMapper()
    val dynamoMapper: DynamoDBMapper = DynamoDBMapper(dbClient)

    @Before fun prepareTest() {
        // insert commonly used test data
        setupStaticBillingData(dbClient)
    }

    @After fun cleanupTest() {
        // delete anything that shouldn't survive any test case
        deleteAllInTable<Account>()
        deleteAllInTable<Organization>()
        deleteAllInTable<Billing>()
    }
    
    private inline fun <reified T: Any> deleteAllInTable() { ... }

    @Test fun testAccountJsonRoundTrip() {
        val acct = Account("123",  ...)
        dynamoMapper.save(acct)

        val item = dynamo.getTable("Accounts").getItem("id", "123")
        val acctReadJson = jsonMapper.readValue<Account>(item.toJSON())
        assertEquals(acct, acctReadJson)
    }

    // ...more test cases

}

注意:示例的某些部分缩写为 ...