adding draining mechanism

Author: mhlidd

utils/config-utils/src/main/java/datadog/trace/config/inversion/ConfigHelper.java

@@ -2,11 +2,14 @@
 
 import datadog.environment.EnvironmentVariables;
 import datadog.trace.api.telemetry.ConfigInversionMetricCollectorProvider;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -49,6 +52,9 @@ public String toString() {
   // Default to production source
   private SupportedConfigurationSource configSource = new SupportedConfigurationSource();
 
+  // Collects unsupported config keys encountered in STRICT_TEST mode
+  private final Set<String> unsupportedConfigs = ConcurrentHashMap.newKeySet();
+
   public static ConfigHelper get() {
     return INSTANCE;
   }
@@ -75,9 +81,18 @@ void resetCache() {
   void resetToDefaults() {
     configSource = new SupportedConfigurationSource();
     this.configInversionStrict = StrictnessPolicy.WARNING;
+    unsupportedConfigs.clear();
     resetCache();
   }
 
+  /** Returns and clears the set of unsupported config keys encountered in STRICT_TEST mode. */
+  public List<String> drainUnsupportedConfigs() {
+    List<String> result = new ArrayList<>(unsupportedConfigs);
+    unsupportedConfigs.clear();
+    Collections.sort(result);
+    return result;
+  }
+
   public static Map<String, String> env() {
     return get().getEnvironmentVariables();
   }
@@ -143,6 +158,7 @@ public String getEnvironmentVariable(String name) {
       }
 
       if (configInversionStrict == StrictnessPolicy.STRICT_TEST) {
+        unsupportedConfigs.add(name);
         throw new IllegalArgumentException(
             "Unsupported configuration: "
                 + name