Add test for child TraceIdRatioBasedSampler warning

Author: Gosling-dude

sdk/trace/src/test/java/io/opentelemetry/sdk/trace/samplers/ParentBasedSamplerBuilderTest.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.sdk.trace.samplers;
+
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.logging.Handler;
+import java.util.logging.Level;
+import java.util.logging.LogRecord;
+import java.util.logging.Logger;
+import org.junit.jupiter.api.Test;
+
+class ParentBasedSamplerBuilderTest {
+
+  @Test
+  void emitsWarningWhenTraceIdRatioBasedUsedAsChildSampler() {
+    Logger logger = Logger.getLogger(ParentBasedSamplerBuilder.class.getName());
+    TestLogHandler handler = new TestLogHandler();
+    logger.addHandler(handler);
+
+    try {
+      Sampler ratioSampler = Sampler.traceIdRatioBased(0.5);
+
+      Sampler.parentBasedBuilder(Sampler.alwaysOn()).setRemoteParentSampled(ratioSampler).build();
+
+      assertTrue(
+          handler.warnings.stream()
+              .anyMatch(
+                  msg ->
+                      msg.contains("TraceIdRatioBasedSampler is being used as a child sampler")));
+    } finally {
+      logger.removeHandler(handler);
+    }
+  }
+
+  static class TestLogHandler extends Handler {
+    final List<String> warnings = new ArrayList<>();
+
+    @Override
+    public void publish(LogRecord record) {
+      if (record.getLevel().equals(Level.WARNING)) {
+        warnings.add(record.getMessage());
+      }
+    }
+
+    @Override
+    public void flush() {}
+
+    @Override
+    public void close() {}
+  }
+}