### Question:
RequestProviderService { @Nullable public String getInstanceId() { return getHeader(INSTANCE_ID); }  Optional<Boolean> resolveTppRedirectPreferred(); RequestData getRequestData(); PsuIdData getPsuIdData(); @NotNull UUID getInternalRequestId(); @Nullable String getInstanceId(); String getInternalRequestIdString(); UUID getRequestId(); String getRequestIdString(); boolean isRequestFromPsu(); boolean isRequestFromTPP(); String getPsuIpAddress(); String getTppRedirectURI(); String getTppNokRedirectURI(); String getOAuth2Token(); String getTppRolesAllowedHeader(); @NotNull String getAcceptHeader(); String getContentTypeHeader(); String getEncodedTppQwacCert(); String getTppBrandLoggingInformationHeader(); Boolean getTppRejectionNoFundsPreferred();  }### Answer:
@Test void getInstanceId() { when(httpServletRequest.getHeader(RequestProviderService.INSTANCE_ID)).thenReturn(INSTANCE_ID); String actual = requestProviderService.getInstanceId(); assertEquals(INSTANCE_ID, actual); }