How to Mock a Static function with WebMvcTest in Springboot - mockito

Question

Is there any functionality within the #WebMvcTest annotation that can be used to test static functions of a class?

Answer 1

Since I believe I found it out (and it's lacking in the baeldung-tutorial linked), here's an example (I don't use #WebMvcTest currently, I am testing a configuration object):
(see below for an explanation)
(imports omitted in favor of brevity)
#Slf4j
#ExtendWith(SpringExtension.class)
#ContextConfiguration(classes = ServerObjectConfiguration.class)
class ServerObjectConfigurationTest {
// 192.168.178.82
private static final byte[] EXAMPLE_IP_V4 = {-64, -88, -78, 82};
// 2001:0db8:85a3:0000:0000:8a2e:0370:7334
private static final byte[] EXAMPLE_IP_V6 = {32, 1, 13, -72, -123, -93, 0, 0, 0, 0, -118, 46, 3, 112, 115, 52};
private static final byte[] EXAMPLE_MAC_ADDRESS = {-68, -48, 116, 9, -47, 11};
private static final MockedStatic<NetworkInterface> mockedNetworkInterface = Mockito.mockStatic(NetworkInterface.class);
private static final MockedStatic<InetAddress> mockedInetAddress = Mockito.mockStatic(InetAddress.class);
#Autowired
private ServerObjectConfiguration serverObjectConfiguration;
#Autowired
private Server server;
#SneakyThrows
#BeforeAll
static void setUp() {
// This is SPARTAAA... or rather: crazy, because everything java.net seems to smell of bad design decisions
InetAddress ipV4InetAddress = mock(InetAddress.class);
when(ipV4InetAddress.getAddress())
.thenReturn(EXAMPLE_IP_V4);
when(ipV4InetAddress.isSiteLocalAddress())
.thenReturn(true);
InetAddress ipV6InetAddress = mock(InetAddress.class);
when(ipV6InetAddress.getAddress())
.thenReturn(EXAMPLE_IP_V6);
when(ipV6InetAddress.isSiteLocalAddress())
.thenReturn(true);
InterfaceAddress ipV4InterfaceAddress = mock(InterfaceAddress.class);
when(ipV4InterfaceAddress.getAddress())
.thenReturn(ipV4InetAddress);
InterfaceAddress ipV6InterfaceAddress = mock(InterfaceAddress.class);
when(ipV6InterfaceAddress.getAddress())
.thenReturn(ipV6InetAddress);
NetworkInterface networkInterface = mock(NetworkInterface.class);
when(networkInterface.getInterfaceAddresses())
.thenReturn(List.of(ipV4InterfaceAddress, ipV6InterfaceAddress));
when(networkInterface.getHardwareAddress())
.thenReturn(EXAMPLE_MAC_ADDRESS);
mockedInetAddress.when(() -> InetAddress.getByAddress(EXAMPLE_IP_V4))
.thenReturn(ipV4InetAddress);
mockedInetAddress.when(() -> InetAddress.getByAddress(EXAMPLE_IP_V6))
.thenReturn(ipV6InetAddress);
mockedNetworkInterface.when(() -> NetworkInterface.getByInetAddress(ipV4InetAddress))
.thenReturn(networkInterface);
mockedNetworkInterface.when(() -> NetworkInterface.getByInetAddress(ipV6InetAddress))
.thenReturn(networkInterface);
mockedNetworkInterface.when(NetworkInterface::networkInterfaces)
.thenReturn(Stream.of(networkInterface));
}
#AfterAll
static void tearDown() {
mockedInetAddress.close();
mockedNetworkInterface.close();
}
#SneakyThrows
#Test
void test_serverObjectIsConfiguredAsExpected() {
// the bean uses NetworkInterface to get the IP-addresses and MAC-address
assertThat(server.getMacAddresses()).containsOnly(EXAMPLE_MAC_ADDRESS);
assertThat(server.getIpAddresses()).containsExactlyInAnyOrder(EXAMPLE_IP_V4, EXAMPLE_IP_V6);
}
}
To mock a static method in a way, that Spring Boot uses it during Bean initialization / context creation, you have to do it in a #BeforeAll (JUnit5) annotated method, which is static. The reason is, that you want to mock the static method as early in your test as you can.
I tried to use a thread-local Mockito#mockStatic call, but since my bean is getting initialized before the test even starts, my attempt at mocking the relevant static methods was too late.
This approach definitely works and the Server-bean, that contains the IP-addresses and the MAC-address, receives the values I am expecting it to.