fleetd/src/test/java/dev/ltms/fleet/FleetdAssemblyFleetAppTest.java

@@ -40,6 +40,14 @@ import static org.junit.jupiter.api.Assertions.assertEquals;
  * FleetAppTwoDaemonTest} already proves {@code FleetApp} itself merges/gates correctly given two
  * clients; the gap this pins is that the assembly actually passes it two.
  *
+ * <p><strong>Both directions, not just one</strong> (fleetd #612 issue comment 17525): the deleted
+ * guard's positive assertion required the exact pair {@code "new FleetApp(herdr, memberHerdr,
+ * workers,"}, which does not survive EITHER daemon being dropped. An earlier version of this class
+ * only proved the member-dropped direction, which left {@code new FleetApp(memberHerdr,
+ * memberHerdr, ...)} — the symmetric bug, {@code /healthz} green while the LEAD daemon is down —
+ * an undetected regression. {@link #healthzGoesRedWhenTheLeadDaemonIsDownEvenThoughTheMemberIsUp}
+ * closes that.
+ *
  * <p>Unlike the {@code ConnectionIdentity} half of CB-185 ({@code
  * FleetdAssemblyConnectionIdentityTest}), {@code /healthz} needs no caller identity at all, so
  * this test can bind {@link FleetdRuntime#app()} to a REAL ephemeral port (exactly {@code
@@ -206,4 +214,24 @@ class FleetdAssemblyFleetAppTest {
 
         assertEquals(200, get(port, "/healthz").statusCode());
     }
+
+    /**
+     * The symmetric pin (fleetd #612 issue comment 17525): the LEAD daemon is down; the MEMBER
+     * daemon is healthy. If the assembly built {@code FleetApp} with only the member client
+     * (dropping {@code herdr} — the mirror of the bug above, {@code new FleetApp(memberHerdr,
+     * memberHerdr, ...)}), the down LEAD is invisible and {@code /healthz} stays 200. Without this
+     * case the pair above is one-directional and does not cover the deleted guard's positive
+     * assertion (it required BOTH {@code herdr,} and {@code memberHerdr,} in that order).
+     */
+    @Test
+    void healthzGoesRedWhenTheLeadDaemonIsDownEvenThoughTheMemberIsUp(@TempDir Path dir) throws Exception {
+        FakeHerdr lead = new FakeHerdr().healthy(false);
+        FakeHerdr member = new FakeHerdr();
+
+        int port = assembleAndBind(dir, lead, member);
+
+        HttpResponse<String> res = get(port, "/healthz");
+        assertEquals(503, res.statusCode(),
+                "a down LEAD daemon must not be masked by a healthy member: " + res.body());
+    }
 }