### Question:
OauthHeaderInterceptor implements Interceptor { @Override public Request.Builder preHandle(Request.Builder builder) { String oauthBankCode = AdapterConfig.readProperty(BANK_CODE_FOR_OAUTH, ""); List<String> bankCodes = Arrays.stream(oauthBankCode.split(",")) .map(String::trim).collect(Collectors.toList()); String requestBankCode = builder.headers().get(RequestHeaders.X_GTW_BANK_CODE); if (oauthBankCode.isEmpty() || !bankCodes.contains(requestBankCode)) { return builder; } String oauthHeaderName = AdapterConfig.readProperty(OAUTH_HEADER_NAME, ""); if (builder.headers().containsKey(oauthHeaderName)) { return builder; } String headerValue = getOauthHeaderValue(bankCodes, requestBankCode); if (!oauthHeaderName.isEmpty() && !headerValue.isEmpty()) { builder.header(oauthHeaderName, headerValue); } return builder; }  @Override Request.Builder preHandle(Request.Builder builder);  }### Answer:
@Test void willNotOverrideHeader() { Request.Builder builder = initRequestBuilder("90001002"); builder.header("X-oauth-PREFERRED", "pre-step"); Request.Builder result = interceptor.preHandle(builder); Assertions.assertEquals("pre-step", result.headers().get(header)); }
@Test void applyRequestBankCodeIsAbsent() { RequestBuilderImpl builder = new RequestBuilderImpl(null, null, null); interceptor.preHandle(builder); Assertions.assertEquals(0, builder.headers().size()); }