Make jmethodID-churn race-detection check a skip, not a fail

Fixes review comment: the counter-delta check is best-effort — a
healthy host that doesn't race unload tightly enough shouldn't flake
CI. Switch it to Assumptions.assumeTrue so a missed race reports as
skipped rather than failed.

Author: jbachorik

ddprof-test/src/test/java/com/datadoghq/profiler/memleak/JMethodIDInvalidationStressTest.java

@@ -15,6 +15,7 @@
  */
 package com.datadoghq.profiler.memleak;
 
+import org.junit.jupiter.api.Assumptions;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.Timeout;
 import org.objectweb.asm.ClassWriter;
@@ -66,9 +67,13 @@
  * native whitebox counters ({@code JavaProfiler#getDebugCounters()}) for {@code
  * jmethodid_skipped_count} and {@code line_number_table_unreadable} -- both are incremented in
  * {@code fillJavaMethodInfo} exactly when {@code SafeAccess::isReadableRange} rejects a stale
- * jmethodID's class/method metadata or line-number table (see flightRecorder.cpp) -- and asserts
- * at least one of them increased during the churn window. A pass therefore means both "no crash"
- * and "a stale jmethodID was actually observed and safely guarded." We cannot run this under ASan
+ * jmethodID's class/method metadata or line-number table (see flightRecorder.cpp) -- and checks
+ * that at least one of them increased during the churn window. Whether the race is actually hit
+ * within the window is JVM/host-discretionary, so that check is a JUnit assumption rather than an
+ * assertion: if neither counter moved, the test is reported as skipped (not failed), since a
+ * healthy host that simply didn't race tightly enough this run is not evidence of a regression. A
+ * pass therefore means both "no crash" and "a stale jmethodID was actually observed and safely
+ * guarded"; a skip means only the former was exercised. We cannot run this under ASan
  * here, since the profiler under test must run as a live JVMTI agent inside the same JVM process
  * the test is driving, not as a standalone ASan-instrumented binary the way the gtest-level native
  * unit tests can.
@@ -169,14 +174,18 @@ public void testProfilerSurvivesConcurrentClassUnloadDuringDump() throws Excepti
       long unreadableLineTableDelta = after.getOrDefault("line_number_table_unreadable", 0L)
           - before.getOrDefault("line_number_table_unreadable", 0L);
 
-      assertTrue(skippedDelta > 0 || unreadableLineTableDelta > 0,
+      // Whether the stale-jmethodID race actually gets hit within the churn window is
+      // JVM/host-discretionary (see class javadoc); treat "never observed" as an aborted
+      // run rather than a failure so a healthy host that just didn't race tightly enough
+      // doesn't flake CI.
+      Assumptions.assumeTrue(skippedDelta > 0 || unreadableLineTableDelta > 0,
           "Churn window completed without the profiler ever encountering a stale/unmapped "
               + "jmethodID (jmethodid_skipped_count delta=" + skippedDelta
               + ", line_number_table_unreadable delta=" + unreadableLineTableDelta
               + ") -- this test is meant to prove the guard actually fires under class-unload "
-              + "churn, not just that the JVM didn't crash; if this keeps failing, the churn "
-              + "isn't racing unload against resolveMethod/fillJavaMethodInfo tightly enough "
-              + "(consider more churn threads or a longer window).");
+              + "churn, not just that the JVM didn't crash; if this keeps getting skipped, the "
+              + "churn isn't racing unload against resolveMethod/fillJavaMethodInfo tightly "
+              + "enough (consider more churn threads or a longer window).");
     } finally {
       running.set(false);
       for (Thread t : churnThreads) {