Add environment property to @SpringBootTest before application.properties evaluation?

Question

Is it possible to add a "dynamic" property from a class to application.properties before they are evaluated?

I want to achieve the following: find a free port on the system, inject it as property mockPort into the spring lifecycle, and reuse this port to override a property from application.properties using @TestPropertySource, as follows:

@SpringBootTest @TestPropertySource(properties = "web.client.url=localhost:${mockPort}/path") public class MyWebTest { //TODO how to write the port into ${mockPort} property? private static final PORT = SocketUtils.findAvailableTcpPort(); @BeforeEach public void init() { MockWebServer mock = new MockWebServer(); mock.start(PORT); } @Test public void test() { service.runWebRequest(); } }

The service under test can be any client that makes use of @Value("${web.client.url}). And as the free port is found dynamically during runtime, I have to somehow inject it into that property.

How can I achieve this?

Andy Wilkinson · Accepted Answer · 2022-01-19 19:15:45Z

You can use Spring Framework's @DynamicPropertySource for this purpose. It's described in this blog post.

In the case of MyWebTest, the dynamic property source would look something like this:

@DynamicPropertySource static void mockPortProperty(DynamicPropertyRegistry registry) { registry.add("mockPort", () -> PORT); }

Chin Huang · Accepted Answer · 2022-01-19 22:58:13Z

Maybe you prefer to start a single MockWebServer for all test classes, instead of starting a new server for each test method. When this class is initialized, the static block starts a server and sets a system property to the server URL. System properties override properties from the application.properties file.

@TestConfiguration public class MockWebServerConfiguration { private static final MockWebServer mockWebServer = new MockWebServer(); static { int port = SocketUtils.findAvailableTcpPort(); mockWebServer.start(port); System.setProperty("web.client.url", "localhost:" + port + "/path"); } }

To include this configuration class in your integration test, annotate your test class with:

@Import(MockWebServerConfiguration.class)

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