### Question:
IdpSelectedStateController implements ErrorResponsePreparedStateController, IdpSelectingStateController, AuthnRequestCapableController, RestartJourneyStateController { public String getMatchingServiceEntityId() { return transactionsConfigProxy.getMatchingServiceEntityId(state.getRequestIssuerEntityId()); } IdpSelectedStateController(
            final IdpSelectedState state,
            final HubEventLogger hubEventLogger,
            final StateTransitionAction stateTransitionAction,
            final IdentityProvidersConfigProxy identityProvidersConfigProxy,
            final TransactionsConfigProxy transactionsConfigProxy,
            final ResponseFromHubFactory responseFromHubFactory,
            final PolicyConfiguration policyConfiguration,
            final AssertionRestrictionsFactory assertionRestrictionsFactory,
            final MatchingServiceConfigProxy matchingServiceConfigProxy); AuthnRequestFromHub getRequestFromHub(); void handleNoAuthenticationContextResponseFromIdp(AuthenticationErrorResponse authenticationErrorResponse); void handlePausedRegistrationResponseFromIdp(String requestIssuerEntityId, String principalIdAsSeenByHub, Optional<LevelOfAssurance> responseLoa, String analyticsSessionId, String journeyType); void handleAuthenticationFailedResponseFromIdp(AuthenticationErrorResponse authenticationErrorResponse); void handleRequesterErrorResponseFromIdp(RequesterErrorResponse requesterErrorResponseDto); void handleMatchingJourneySuccessResponseFromIdp(SuccessFromIdp successFromIdp); void handleNonMatchingJourneySuccessResponseFromIdp(SuccessFromIdp successFromIdp); void handleFraudResponseFromIdp(FraudFromIdp fraudFromIdp); AttributeQueryRequestDto createAttributeQuery(SuccessFromIdp successFromIdp); @Override ResponseFromHub getErrorResponse(); boolean isRegistrationContext(); String getMatchingServiceEntityId(); boolean isMatchingJourney(); @Override void handleIdpSelected(String idpEntityId, String principalIpAddress, boolean registering, LevelOfAssurance requestedLoa, String analyticsSessionId, String journeyType, String abTestVariant); @Override String getRequestIssuerId(); @Override AuthnRequestSignInProcess getSignInProcessDetails(); @Override void transitionToSessionStartedState();  }### Answer:
@Test public void shouldReturnMatchingServiceEntityIdWhenAsked() { controller.getMatchingServiceEntityId(); verify(transactionsConfigProxy).getMatchingServiceEntityId(idpSelectedState.getRequestIssuerEntityId()); }