fix: remove dead code from createPerformanceCard, fix CSV zero-value bug, add differential tests

- Remove unreachable avgResponseTime/lastExecutionTime branches from
  createPerformanceCard (its metrics list only has memory/CPU/disk/network keys)
- Fix CSV export treating avg_response_time=0 as N/A by using != null
  instead of truthiness check, consistent with table rendering
- Fix trailing whitespace in updateTableRows
- Update modularized test assertion for ×1000 conversion (150 → 150000)
- Add JS tests for createMetricsCard: seconds→ms conversion, ISO datetime
  formatting, null handling, zero-value preservation
- Add Python test verifying build_top_performers preserves 0.0 values

Closes #3793, Closes #3580

Signed-off-by: Mihai Criveti <crivetimihai@gmail.com>

Author: crivetimihai

mcpgateway/admin_ui/metrics.js

@@ -1494,7 +1494,7 @@ export const updateTableRows = function (
     avgTimeCell.className =
       "px-6 py-4 whitespace-nowrap text-sm text-gray-500 dark:text-gray-300 sm:px-6 sm:py-4";
     const avgTime = item.avg_response_time ?? item.avgResponseTime;
-    avgTimeCell.textContent = avgTime != null ? `${Math.round(Number(avgTime) * 1000)}ms` : "N/A" ;
+    avgTimeCell.textContent = avgTime != null ? `${Math.round(Number(avgTime) * 1000)}ms` : "N/A";
     row.appendChild(avgTimeCell);
 
     // Success Rate
@@ -1554,7 +1554,7 @@ item.execution_count ||
 item.executions ||
 0,
 ),
-item.avg_response_time ?? item.avgResponseTime
+(item.avg_response_time ?? item.avgResponseTime) != null
 ? `${Math.round((item.avg_response_time ?? item.avgResponseTime) * 1000)}ms`
 : "N/A",
 `${calculateSuccessRate(item)}%`,
@@ -1659,20 +1659,7 @@ export const createPerformanceCard = function (performanceData) {
 
       const valueSpan = document.createElement("span");
       valueSpan.className = "font-medium dark:text-gray-200";
-      let displayValue;
-      if (value === "N/A") {
-        displayValue = "N/A";
-      } else if (metric.key === "avgResponseTime") {
-        const ms = Number(value);
-        displayValue = isNaN(ms) ? "N/A" : `${(ms * 1000).toFixed(1)} ms`;
-      } else if (metric.key === "lastExecutionTime") {
-        displayValue = typeof value === "string" && value.includes("T")
-          ? value.slice(0, 16).replace("T", " ")
-          : String(value);
-      } else {
-        displayValue = String(value);
-      }
-      valueSpan.textContent = displayValue;
+      valueSpan.textContent = value === "N/A" ? "N/A" : String(value);
 
       metricRow.appendChild(label);
       metricRow.appendChild(valueSpan);

tests/unit/js/metrics.test.js

@@ -609,7 +609,7 @@ describe("extractKPIData", () => {
     };
 
     const kpi = extractKPIData(data);
-    expect(kpi.avgResponseTime).toBe(150); // Weighted average
+    expect(kpi.avgResponseTime).toBe(150000); // Weighted average (seconds × 1000 → ms)
   });
 
   test("handles null avgResponseTime", () => {
@@ -825,6 +825,7 @@ describe("createPerformanceCard", () => {
     expect(card).toBeInstanceOf(HTMLElement);
     consoleError.mockRestore();
   });
+
 });
 
 describe("createRecentActivitySection", () => {
@@ -904,6 +905,31 @@ describe("createMetricsCard", () => {
     const card = createMetricsCard("Prompts", {});
     expect(card.textContent).toContain("N/A");
   });
+
+  test("converts avgResponseTime from seconds to milliseconds", () => {
+    const metrics = { avgResponseTime: 1.5 };
+    const card = createMetricsCard("Tools", metrics);
+    expect(card.textContent).toContain("1500.0 ms");
+  });
+
+  test("formats lastExecutionTime as human-readable date", () => {
+    const metrics = { lastExecutionTime: "2026-03-13T06:00:00.000000" };
+    const card = createMetricsCard("Tools", metrics);
+    expect(card.textContent).toContain("2026-03-13 06:00");
+  });
+
+  test("displays N/A for null avgResponseTime", () => {
+    const metrics = { avgResponseTime: null };
+    const card = createMetricsCard("Tools", metrics);
+    // avgResponseTime null → value resolves to "N/A" via ?? chain
+    expect(card.textContent).toContain("N/A");
+  });
+
+  test("preserves zero avgResponseTime", () => {
+    const metrics = { avgResponseTime: 0 };
+    const card = createMetricsCard("Tools", metrics);
+    expect(card.textContent).toContain("0.0 ms");
+  });
 });
 
 // ===================================================================

tests/unit/mcpgateway/utils/test_metrics_common.py

@@ -44,3 +44,20 @@ def test_build_top_performers_handles_missing_values():
     assert performers[0].avg_response_time is None
     assert performers[0].success_rate is None
     assert performers[0].last_execution is None
+
+
+def test_build_top_performers_preserves_zero_values():
+    """Zero avg_response_time and success_rate must not be coerced to None."""
+    result = SimpleNamespace(
+        id=3,
+        name="zero-tool",
+        execution_count=10,
+        avg_response_time=0.0,
+        success_rate=0.0,
+        last_execution=None,
+    )
+
+    performers = build_top_performers([result])
+
+    assert performers[0].avg_response_time == 0.0
+    assert performers[0].success_rate == 0.0