diff --git a/test/relay-health-thresholds.test.mjs b/test/relay-health-thresholds.test.mjs
index fe5e9be..0ad9ec9 100644
--- a/test/relay-health-thresholds.test.mjs
+++ b/test/relay-health-thresholds.test.mjs
@@ -13,38 +13,159 @@ function entry(timestamp, healthyRelays, totalRelays = 3) {
   };
 }
 
-test('raises all-relays-down duration alert after threshold', () => {
+test('evaluateAlertThresholds', async (t) => {
   const now = Date.parse('2026-02-15T12:00:00Z');
-  const history = [
-    entry('2026-02-15T11:30:00Z', 1),
-    entry('2026-02-15T11:45:00Z', 0),
-    entry('2026-02-15T11:55:00Z', 0),
-    entry('2026-02-15T12:00:00Z', 0),
-  ];
+  const minute = 60_000;
 
-  const current = history[history.length - 1];
-  const result = evaluateAlertThresholds(current, history, {
-    allRelaysDownMinutes: 10,
-    minSuccessRate: 0.1,
-    windowMinutes: 60,
-  }, { nowMs: now });
+  await t.test('Happy Path: No alerts when thresholds are not met', () => {
+    const history = [
+      entry(new Date(now - 10 * minute).toISOString(), 3),
+      entry(new Date(now).toISOString(), 3),
+    ];
+    const current = history[history.length - 1];
 
-  assert.ok(result.alerts.some((alert) => alert.type === 'all_relays_down_duration'));
-});
-
-test('raises success-rate alert when rolling health falls below threshold', () => {
-  const history = [
-    entry('2026-02-15T11:50:00Z', 3),
-    entry('2026-02-15T11:55:00Z', 0),
-    entry('2026-02-15T12:00:00Z', 0),
-  ];
-  const current = history[history.length - 1];
-
-  const result = evaluateAlertThresholds(current, history, {
-    allRelaysDownMinutes: 999,
-    minSuccessRate: 0.5,
-    windowMinutes: 30,
-  }, { nowMs: Date.parse('2026-02-15T12:00:00Z') });
-
-  assert.ok(result.alerts.some((alert) => alert.type === 'relay_success_rate_below_threshold'));
+    const result = evaluateAlertThresholds(current, history, {
+      allRelaysDownMinutes: 10,
+      minSuccessRate: 0.5,
+      windowMinutes: 60,
+    }, { nowMs: now });
+
+    assert.equal(result.alerts.length, 0);
+  });
+
+  await t.test('All Relays Down: Triggers alert when duration equals threshold', () => {
+    // 10 minutes down exactly
+    const history = [
+      entry(new Date(now - 10 * minute).toISOString(), 3), // healthy 10 mins ago
+      entry(new Date(now - 5 * minute).toISOString(), 0),
+      entry(new Date(now).toISOString(), 0),
+    ];
+    const current = history[history.length - 1];
+
+    const result = evaluateAlertThresholds(current, history, {
+      allRelaysDownMinutes: 10,
+      minSuccessRate: 0.1,
+      windowMinutes: 60,
+    }, { nowMs: now });
+
+    const alert = result.alerts.find(a => a.type === 'all_relays_down_duration');
+    assert.ok(alert);
+    assert.equal(alert.actualMinutes, 10);
+  });
+
+  await t.test('All Relays Down: Does NOT trigger alert just below threshold', () => {
+    // 9 minutes down
+    const history = [
+      entry(new Date(now - 9 * minute).toISOString(), 3), // healthy 9 mins ago
+      entry(new Date(now).toISOString(), 0),
+    ];
+    const current = history[history.length - 1];
+
+    const result = evaluateAlertThresholds(current, history, {
+      allRelaysDownMinutes: 10,
+      minSuccessRate: 0.1,
+      windowMinutes: 60,
+    }, { nowMs: now });
+
+    const alert = result.alerts.find(a => a.type === 'all_relays_down_duration');
+    assert.equal(alert, undefined);
+  });
+
+  await t.test('Success Rate: Triggers alert when rate is strictly below threshold', () => {
+    const history = [
+      entry(new Date(now).toISOString(), 1, 4), // 25% healthy
+    ];
+    const current = history[history.length - 1];
+    // Threshold 0.3 > 0.25 -> Alert
+
+    const result = evaluateAlertThresholds(current, history, {
+      allRelaysDownMinutes: 999,
+      minSuccessRate: 0.3,
+      windowMinutes: 60,
+    }, { nowMs: now });
+
+    const alert = result.alerts.find(a => a.type === 'relay_success_rate_below_threshold');
+    assert.ok(alert);
+    assert.equal(alert.actual, 0.25);
+  });
+
+  await t.test('Success Rate: Does NOT trigger alert when rate equals threshold', () => {
+    const history = [
+      entry(new Date(now).toISOString(), 1, 4), // 25% healthy
+    ];
+    const current = history[history.length - 1];
+    // Threshold 0.25 == 0.25 -> No Alert
+
+    const result = evaluateAlertThresholds(current, history, {
+      allRelaysDownMinutes: 999,
+      minSuccessRate: 0.25,
+      windowMinutes: 60,
+    }, { nowMs: now });
+
+    const alert = result.alerts.find(a => a.type === 'relay_success_rate_below_threshold');
+    assert.equal(alert, undefined);
+  });
+
+  await t.test('Success Rate: Does NOT trigger alert when rate is above threshold', () => {
+    const history = [
+      entry(new Date(now).toISOString(), 3, 4), // 75% healthy
+    ];
+    const current = history[history.length - 1];
+    // Threshold 0.5 < 0.75 -> No Alert
+
+    const result = evaluateAlertThresholds(current, history, {
+      allRelaysDownMinutes: 999,
+      minSuccessRate: 0.5,
+      windowMinutes: 60,
+    }, { nowMs: now });
+
+    const alert = result.alerts.find(a => a.type === 'relay_success_rate_below_threshold');
+    assert.equal(alert, undefined);
+  });
+
+  await t.test('Multiple Alerts: Both conditions met', () => {
+    // Down for 20 mins (threshold 10) AND rate 0 (threshold 0.5)
+    const history = [
+      entry(new Date(now - 20 * minute).toISOString(), 3), // Healthy 20m ago
+      entry(new Date(now - 10 * minute).toISOString(), 0),
+      entry(new Date(now).toISOString(), 0),
+    ];
+    const current = history[history.length - 1];
+
+    const result = evaluateAlertThresholds(current, history, {
+      allRelaysDownMinutes: 10,
+      minSuccessRate: 0.5,
+      windowMinutes: 60,
+    }, { nowMs: now });
+
+    assert.equal(result.alerts.length, 2);
+    assert.ok(result.alerts.some(a => a.type === 'all_relays_down_duration'));
+    assert.ok(result.alerts.some(a => a.type === 'relay_success_rate_below_threshold'));
+  });
+
+  await t.test('Edge Case: Empty history (should not crash)', () => {
+    const history = [];
+    const current = entry(new Date(now).toISOString(), 3); // current result is healthy
+
+    const result = evaluateAlertThresholds(current, history, {
+      allRelaysDownMinutes: 10,
+      minSuccessRate: 0.5,
+      windowMinutes: 60,
+    }, { nowMs: now });
+
+    assert.equal(result.alerts.length, 0);
+  });
+
+  await t.test('Edge Case: Empty history but current result is unhealthy', () => {
+    const history = [];
+    const current = entry(new Date(now).toISOString(), 0); // current result is unhealthy
+
+    const result = evaluateAlertThresholds(current, history, {
+      allRelaysDownMinutes: 10,
+      minSuccessRate: 0.5,
+      windowMinutes: 60,
+    }, { nowMs: now });
+
+    assert.equal(result.alerts.length, 0);
+  });
 });