Refresh performance metrics in assertions

Add Page.RefreshPerformanceMetricsAsync to re-read window.__motusPerf via Runtime.evaluate and merge values into LastPerformanceMetrics (uses System.Text.Json and a ReadPerfScript). Call this refresh from all page performance assertions (LCP, FCP, TTFB, CLS, INP) so retries can pick up metrics that arrive after initial collection. Update sample tests to use Fixtures.SetPageContentAsync(SimplePage) instead of navigating to example.com and remove the Integration TestCategory from these tests.

Author: TorreyBetts

samples/Motus.Samples/Tests/PerformanceTests.cs

@@ -40,27 +40,23 @@ public async Task MethodAttribute_OverridesClassBudget()
     }
 
     [TestMethod]
-    [TestCategory("Integration")]
     public async Task LcpBelow_IndividualMetricAssertion()
     {
-        // Individual metric assertions require a real HTTP origin for Web Vitals to fire.
-        await Page.GotoAsync("https://example.com");
+        await Fixtures.SetPageContentAsync(Page, SimplePage);
         await Expect.That(Page).ToHaveLcpBelowAsync(5000);
     }
 
     [TestMethod]
-    [TestCategory("Integration")]
     public async Task FcpBelow_IndividualMetricAssertion()
     {
-        await Page.GotoAsync("https://example.com");
+        await Fixtures.SetPageContentAsync(Page, SimplePage);
         await Expect.That(Page).ToHaveFcpBelowAsync(5000);
     }
 
     [TestMethod]
-    [TestCategory("Integration")]
     public async Task ClsBelow_NoLayoutShift()
     {
-        await Page.GotoAsync("https://example.com");
+        await Fixtures.SetPageContentAsync(Page, SimplePage);
         await Expect.That(Page).ToHaveClsBelowAsync(0.5);
     }
 

src/Motus/Assertions/PageAssertions.cs

@@ -87,6 +87,7 @@ public async Task ToMeetPerformanceBudgetAsync(AssertionOptions? options = null)
 
         await RetryAsync(async ct =>
         {
+            await _page.RefreshPerformanceMetricsAsync().ConfigureAwait(false);
             var metrics = _page.LastPerformanceMetrics;
             if (metrics is null)
                 return (false, "<no metrics collected>");
@@ -103,6 +104,7 @@ await RetryAsync(async ct =>
     public Task ToHaveLcpBelowAsync(double thresholdMs, AssertionOptions? options = null) =>
         RetryAsync(async ct =>
         {
+            await _page.RefreshPerformanceMetricsAsync().ConfigureAwait(false);
             var metrics = _page.LastPerformanceMetrics;
             if (metrics?.Lcp is null)
                 return (false, "<LCP not collected>");
@@ -113,6 +115,7 @@ public Task ToHaveLcpBelowAsync(double thresholdMs, AssertionOptions? options =
     public Task ToHaveFcpBelowAsync(double thresholdMs, AssertionOptions? options = null) =>
         RetryAsync(async ct =>
         {
+            await _page.RefreshPerformanceMetricsAsync().ConfigureAwait(false);
             var metrics = _page.LastPerformanceMetrics;
             if (metrics?.Fcp is null)
                 return (false, "<FCP not collected>");
@@ -123,6 +126,7 @@ public Task ToHaveFcpBelowAsync(double thresholdMs, AssertionOptions? options =
     public Task ToHaveTtfbBelowAsync(double thresholdMs, AssertionOptions? options = null) =>
         RetryAsync(async ct =>
         {
+            await _page.RefreshPerformanceMetricsAsync().ConfigureAwait(false);
             var metrics = _page.LastPerformanceMetrics;
             if (metrics?.Ttfb is null)
                 return (false, "<TTFB not collected>");
@@ -133,6 +137,7 @@ public Task ToHaveTtfbBelowAsync(double thresholdMs, AssertionOptions? options =
     public Task ToHaveClsBelowAsync(double threshold, AssertionOptions? options = null) =>
         RetryAsync(async ct =>
         {
+            await _page.RefreshPerformanceMetricsAsync().ConfigureAwait(false);
             var metrics = _page.LastPerformanceMetrics;
             if (metrics?.Cls is null)
                 return (false, "<CLS not collected>");
@@ -143,6 +148,7 @@ public Task ToHaveClsBelowAsync(double threshold, AssertionOptions? options = nu
     public Task ToHaveInpBelowAsync(double thresholdMs, AssertionOptions? options = null) =>
         RetryAsync(async ct =>
         {
+            await _page.RefreshPerformanceMetricsAsync().ConfigureAwait(false);
             var metrics = _page.LastPerformanceMetrics;
             if (metrics?.Inp is null)
                 return (false, "<INP not collected>");

src/Motus/Page/Page.Performance.cs

@@ -1,9 +1,14 @@
+using System.Text.Json;
 using Motus.Abstractions;
 
 namespace Motus;
 
 internal sealed partial class Page
 {
+    private const string ReadPerfScript = """
+        JSON.stringify(window.__motusPerf || { lcp: null, cls: 0, inp: null, layoutShifts: [], fcp: null })
+        """;
+
     /// <summary>
     /// The most recent performance metrics, set by <see cref="PerformanceMetricsCollector"/>
     /// after navigation or page close. Null when the hook is disabled or no collection has run.
@@ -15,4 +20,60 @@ internal sealed partial class Page
     /// from <see cref="PerformanceBudgetAttribute"/> resolution.
     /// </summary>
     internal PerformanceBudget? ActivePerformanceBudget { get; set; }
+
+    /// <summary>
+    /// Re-reads the PerformanceObserver data from the page and updates
+    /// <see cref="LastPerformanceMetrics"/>. Called by assertions during retry
+    /// to pick up metrics that arrived after the initial post-navigation collection.
+    /// </summary>
+    internal async Task RefreshPerformanceMetricsAsync()
+    {
+        try
+        {
+            var evalResult = await _session.SendAsync(
+                "Runtime.evaluate",
+                new RuntimeEvaluateParams(ReadPerfScript, ReturnByValue: true),
+                CdpJsonContext.Default.RuntimeEvaluateParams,
+                CdpJsonContext.Default.RuntimeEvaluateResult,
+                CancellationToken.None).ConfigureAwait(false);
+
+            if (evalResult.ExceptionDetails is not null || evalResult.Result.Value is not { } jsonValue)
+                return;
+
+            var json = jsonValue.GetString();
+            if (json is null)
+                return;
+
+            using var doc = JsonDocument.Parse(json);
+            var root = doc.RootElement;
+
+            var existing = LastPerformanceMetrics;
+
+            double? lcp = existing?.Lcp, fcp = existing?.Fcp, cls = existing?.Cls, inp = existing?.Inp;
+
+            if (root.TryGetProperty("lcp", out var lcpEl) && lcpEl.ValueKind == JsonValueKind.Number)
+                lcp = lcpEl.GetDouble();
+            if (root.TryGetProperty("fcp", out var fcpEl) && fcpEl.ValueKind == JsonValueKind.Number)
+                fcp = fcpEl.GetDouble();
+            if (root.TryGetProperty("cls", out var clsEl) && clsEl.ValueKind == JsonValueKind.Number)
+                cls = clsEl.GetDouble();
+            if (root.TryGetProperty("inp", out var inpEl) && inpEl.ValueKind == JsonValueKind.Number)
+                inp = inpEl.GetDouble();
+
+            LastPerformanceMetrics = new PerformanceMetrics(
+                Lcp: lcp,
+                Fcp: fcp,
+                Ttfb: existing?.Ttfb,
+                Cls: cls,
+                Inp: inp,
+                JsHeapSize: existing?.JsHeapSize,
+                DomNodeCount: existing?.DomNodeCount,
+                LayoutShifts: existing?.LayoutShifts ?? [],
+                CollectedAtUtc: DateTime.UtcNow);
+        }
+        catch
+        {
+            // Best effort; keep existing metrics
+        }
+    }
 }