Enhance AgentVoqSwitchWithMultipleDsfNodesTest tests to work in multi-switch mode

Summary:
Hw_agent_tests use fb303 counters to do the tests. In mono mode, this is simply a call to wedge-agent binary. However, tests don't work in multi mode, since these counters are not available in the sw-agent.
For multi-switch mode, get the the client to hwAgent cached in SwSwitch for
 the hwAgent, and call getRegexCounters on it.

Reviewed By: msomasundaran

Differential Revision:
D74614472

Privacy Context Container: L1125642

fbshipit-source-id: 39b199cbde1fc2153213562fbc5a41234836d33d

Author: Ashutosh Grewal

fboss/agent/test/AgentEnsemble.cpp

@@ -731,6 +731,30 @@ std::map<std::string, int64_t> AgentEnsemble::getFb303CountersByRegex(
   return counters;
 }
 
+/**
+ * Retrieves the value of a specific fb303 counter for a given switch.
+ *
+ * @details
+ * Works in both mono-switch and multi-switch environments.
+ *
+ * @param key The name of the counter to retrieve.
+ * @param switchID The ID of the switch for which to retrieve the counter.
+ *
+ * @return The value of the specified counter.
+ */
+int64_t AgentEnsemble::getFb303Counter(
+    const std::string& key,
+    const SwitchID& switchID) {
+  int64_t counter{0};
+#ifndef IS_OSS
+  auto client = getSw()->getHwSwitchThriftClientTable()->getClient(switchID);
+  apache::thrift::Client<facebook::thrift::Monitor> monitoringClient{
+      client->getChannelShared()};
+  counter = monitoringClient.sync_getCounter(key);
+#endif
+  return counter;
+}
+
 /**
  * Retrieves the value of the first counter that matches a given regex pattern
  * for a specific port.

fboss/agent/test/AgentEnsemble.h

@@ -322,17 +322,30 @@ class AgentEnsemble : public TestEnsembleIf {
       const std::string& regex);
 
   /**
-   * Retrieves the value of the first counter that matches a given regex pattern
-   * for a specific port.
+   * Retrieves the value of a specific fb303 counter for a given switch.
+   *
+   * @details
+   * Works in both mono-switch and multi-switch environments.
+   *
+   * @param key The name of the counter to retrieve.
+   * @param switchID The ID of the switch for which to retrieve the counter.
+   *
+   * @return The value of the specified counter.
+   */
+  int64_t getFb303Counter(const std::string& key, const SwitchID& switchID);
+
+  /**
+   * Retrieves the value of the first counter that matches a given regex
+   * pattern for a specific port.
    *
    * @details
    * Works in both mono-switch and multi-switch environments.
    *
    * @param portId The ID of the port for which to retrieve the counter.
    * @param regex The regex pattern to match against counter names.
    *
-   * @return The value of the first matching counter if one exists, otherwise
-   * nullopt.
+   * @return The value of the first matching counter if one exists,
+   * otherwise nullopt.
    */
   std::optional<int64_t> getFb303CounterIfExists(
       const PortID& portId,

fboss/agent/test/agent_hw_tests/AgentVoqSwitchWithMultipleDsfNodesTests.cpp

@@ -88,9 +88,13 @@ TEST_F(AgentVoqSwitchWithMultipleDsfNodesTest, remoteSystemPort) {
     // keeping remote switch id passed below in sync with it
     int numCores =
         checkSameAndGetAsic(getAgentEnsemble()->getL3Asics())->getNumCores();
-    auto getStats = [] {
+    auto getStats = [this] {
+      auto switchID = *getSw()->getHwAsicTable()->getSwitchIDs().begin();
       return std::make_tuple(
-          fbData->getCounter(kSystemPortsFree), fbData->getCounter(kVoqsFree));
+          getAgentEnsemble()->getFb303Counter(
+              std::string(kSystemPortsFree), switchID),
+          getAgentEnsemble()->getFb303Counter(
+              std::string(kVoqsFree), switchID));
     };
     auto [beforeSysPortsFree, beforeVoqsFree] = getStats();
     applyNewState([&](const std::shared_ptr<SwitchState>& in) {