diff --git a/products/metrics/metrics-lib/build.gradle.kts b/products/metrics/metrics-lib/build.gradle.kts
index ae38432669a..4f58777ff02 100644
--- a/products/metrics/metrics-lib/build.gradle.kts
+++ b/products/metrics/metrics-lib/build.gradle.kts
@@ -36,15 +36,8 @@ tasks.named<ShadowJar>("shadowJar") {
 extra["minimumBranchCoverage"] = 0.5
 extra["minimumInstructionCoverage"] = 0.8
 extra["excludedClassesCoverage"] = listOf(
-  "datadog.communication.monitor.DDAgentStatsDConnection",
-  "datadog.communication.monitor.DDAgentStatsDConnection.*",
-  "datadog.communication.monitor.LoggingStatsDClient",
+  "datadog.metrics.impl.statsd.DDAgentStatsDClientManager",
+  "datadog.metrics.impl.statsd.DDAgentStatsDConnection",
+  "datadog.metrics.impl.statsd.DDAgentStatsDConnection.*",
+  "datadog.metrics.impl.statsd.LoggingStatsDClient",
 )
-// val excludedClassesBranchCoverage by extra(
-//   listOf(
-//   )
-// )
-// val excludedClassesInstructionCoverage by extra(
-//   listOf(
-//   )
-// )
diff --git a/products/metrics/metrics-lib/src/test/java/datadog/metrics/impl/DDSketchHistogramsTest.java b/products/metrics/metrics-lib/src/test/java/datadog/metrics/impl/DDSketchHistogramsTest.java
new file mode 100644
index 00000000000..d5e87846495
--- /dev/null
+++ b/products/metrics/metrics-lib/src/test/java/datadog/metrics/impl/DDSketchHistogramsTest.java
@@ -0,0 +1,91 @@
+package datadog.metrics.impl;
+
+import static java.util.Arrays.asList;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import datadog.metrics.impl.DDSketchHistograms.ExplicitBoundaries;
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+class DDSketchHistogramsTest {
+
+  // boundaries define 4 bins:
+  //   bin 0: (-inf, 10]
+  //   bin 1: (10,   20]
+  //   bin 2: (20,   30]
+  //   bin 3: (30,  +inf)
+  private static final List<Double> BOUNDARIES = asList(10.0, 20.0, 30.0);
+
+  @Test
+  void indexBelowFirstBoundary() {
+    ExplicitBoundaries eb = new ExplicitBoundaries(BOUNDARIES);
+    assertEquals(0, eb.index(5.0));
+  }
+
+  @Test
+  void indexOnBoundary() {
+    ExplicitBoundaries eb = new ExplicitBoundaries(BOUNDARIES);
+    assertEquals(0, eb.index(10.0));
+    assertEquals(1, eb.index(20.0));
+    assertEquals(2, eb.index(30.0));
+  }
+
+  @Test
+  void indexBetweenBoundaries() {
+    ExplicitBoundaries eb = new ExplicitBoundaries(BOUNDARIES);
+    assertEquals(1, eb.index(15.0));
+    assertEquals(2, eb.index(25.0));
+  }
+
+  @Test
+  void indexAboveLastBoundary() {
+    ExplicitBoundaries eb = new ExplicitBoundaries(BOUNDARIES);
+    assertEquals(3, eb.index(35.0));
+  }
+
+  @Test
+  void lowerBoundOfFirstBinIsNegativeInfinity() {
+    ExplicitBoundaries eb = new ExplicitBoundaries(BOUNDARIES);
+    assertEquals(Double.NEGATIVE_INFINITY, eb.lowerBound(0));
+  }
+
+  @Test
+  void lowerBoundMapsToPreceeedingBoundary() {
+    ExplicitBoundaries eb = new ExplicitBoundaries(BOUNDARIES);
+    assertEquals(10.0, eb.lowerBound(1));
+    assertEquals(20.0, eb.lowerBound(2));
+    assertEquals(30.0, eb.lowerBound(3));
+  }
+
+  @Test
+  void upperBoundMapsToCorrespondingBoundary() {
+    ExplicitBoundaries eb = new ExplicitBoundaries(BOUNDARIES);
+    assertEquals(10.0, eb.upperBound(0));
+    assertEquals(20.0, eb.upperBound(1));
+    assertEquals(30.0, eb.upperBound(2));
+  }
+
+  @Test
+  void upperBoundOfLastBinIsPositiveInfinity() {
+    ExplicitBoundaries eb = new ExplicitBoundaries(BOUNDARIES);
+    assertEquals(Double.POSITIVE_INFINITY, eb.upperBound(3));
+  }
+
+  @Test
+  void extremeIndexableValues() {
+    ExplicitBoundaries eb = new ExplicitBoundaries(BOUNDARIES);
+    assertEquals(Double.NEGATIVE_INFINITY, eb.minIndexableValue());
+    assertEquals(Double.POSITIVE_INFINITY, eb.maxIndexableValue());
+  }
+
+  @Test
+  void unsupportedOperationsThrow() {
+    ExplicitBoundaries eb = new ExplicitBoundaries(BOUNDARIES);
+    assertThrows(UnsupportedOperationException.class, () -> eb.value(0));
+    assertThrows(UnsupportedOperationException.class, eb::relativeAccuracy);
+    assertThrows(UnsupportedOperationException.class, () -> eb.encode(null));
+    assertThrows(UnsupportedOperationException.class, eb::serializedSize);
+    assertThrows(UnsupportedOperationException.class, () -> eb.serialize(null));
+  }
+}
diff --git a/products/metrics/metrics-lib/src/test/java/datadog/metrics/impl/ThreadLocalRecordingTest.java b/products/metrics/metrics-lib/src/test/java/datadog/metrics/impl/ThreadLocalRecordingTest.java
new file mode 100644
index 00000000000..f533355eb89
--- /dev/null
+++ b/products/metrics/metrics-lib/src/test/java/datadog/metrics/impl/ThreadLocalRecordingTest.java
@@ -0,0 +1,86 @@
+package datadog.metrics.impl;
+
+import static java.util.Arrays.asList;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import datadog.metrics.api.Recording;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.CountDownLatch;
+import org.junit.jupiter.api.Test;
+
+class ThreadLocalRecordingTest {
+
+  @Test
+  void delegatesPerThread() throws Exception {
+    Map<Thread, List<String>> callsByThread = new ConcurrentHashMap<>();
+
+    ThreadLocal<Recording> sink =
+        ThreadLocal.withInitial(
+            () -> {
+              List<String> calls = new ArrayList<>();
+              callsByThread.put(Thread.currentThread(), calls);
+              return recordCalls(calls);
+            });
+
+    Recording recording = new ThreadLocalRecording(sink);
+
+    int threadCount = 4;
+    CountDownLatch ready = new CountDownLatch(threadCount);
+    CountDownLatch done = new CountDownLatch(threadCount);
+    Thread[] threads = new Thread[threadCount];
+
+    for (int i = 0; i < threadCount; i++) {
+      threads[i] =
+          new Thread(
+              () -> {
+                ready.countDown();
+                try {
+                  ready.await();
+                } catch (InterruptedException e) {
+                  Thread.currentThread().interrupt();
+                  return;
+                }
+                recording.start();
+                recording.reset();
+                recording.stop();
+                recording.flush();
+                done.countDown();
+              });
+      threads[i].start();
+    }
+    done.await();
+
+    assertEquals(threadCount, callsByThread.size(), "each thread should have its own Recording");
+    for (List<String> calls : callsByThread.values()) {
+      assertEquals(asList("start", "reset", "stop", "flush"), calls);
+    }
+  }
+
+  private static Recording recordCalls(List<String> calls) {
+    return new Recording() {
+      @Override
+      public Recording start() {
+        calls.add("start");
+        return this;
+      }
+
+      @Override
+      public void reset() {
+        calls.add("reset");
+      }
+
+      @Override
+      public void stop() {
+        calls.add("stop");
+      }
+
+      @Override
+      public void flush() {
+        calls.add("flush");
+      }
+    };
+  }
+}