JUNIT 5: Inject spring components to custom TestTemplateInvocationContextProvider - spring

Question

Is there a way in JUnit Jupiter (JUnit 5) that makes it possible to inject Spring components into a TestTemplateInvocationContextProvider?

Answer 1

Yes, if you register your TestTemplateInvocationContextProvider as a bean in the Spring ApplicationContext loaded for your test class, you can then have the provider #Autowired into a field and registered as a JUnit Jupiter extension using #RegisterExtension. The trick is that you'll need to use the per-class test instance lifecycle mode in order for the provider to be registered early enough for JUnit Jupiter to use it.
The following is a modified version of TestTemplateDemo from the JUnit 5 User Guide.
The tests pass "as is", but you can remove the // from the #Bean declaration for the baz bean to see a test fail.
#SpringJUnitConfig
#TestInstance(Lifecycle.PER_CLASS)
class TestTemplateDemo {
#Autowired
#RegisterExtension
TestTemplateInvocationContextProvider testTemplateInvocationContextProvider;
#TestTemplate
void testTemplate(String parameter) {
assertTrue("foo".equals(parameter) || "bar".equals(parameter));
}
#Configuration
static class Config {
#Bean
String foo() {
return "foo";
}
#Bean
String bar() {
return "bar";
}
// #Bean
String baz() {
return "baz";
}
#Bean
TestTemplateInvocationContextProvider myTestTemplateInvocationContextProvider(
List<String> parameters) {
return new MyTestTemplateInvocationContextProvider(parameters);
}
}
public static class MyTestTemplateInvocationContextProvider
implements TestTemplateInvocationContextProvider {
private final List<String> parameters;
public MyTestTemplateInvocationContextProvider(List<String> parameters) {
this.parameters = parameters;
}
#Override
public boolean supportsTestTemplate(ExtensionContext context) {
return true;
}
#Override
public Stream<TestTemplateInvocationContext> provideTestTemplateInvocationContexts(
ExtensionContext context) {
return this.parameters.stream().map(p -> invocationContext(p));
}
private TestTemplateInvocationContext invocationContext(String parameter) {
return new TestTemplateInvocationContext() {
#Override
public String getDisplayName(int invocationIndex) {
return parameter;
}
#Override
public List<Extension> getAdditionalExtensions() {
return Collections.singletonList(new ParameterResolver() {
#Override
public boolean supportsParameter(
ParameterContext parameterContext,
ExtensionContext extensionContext) {
return parameterContext.getParameter().getType().equals(
String.class);
}
#Override
public Object resolveParameter(ParameterContext parameterContext,
ExtensionContext extensionContext) {
return parameter;
}
});
}
};
}
}
}