feat(report): trend charts on the HTML dashboard

src/main/java/com/seleniumboot/reporting/HtmlReportGenerator.java

@@ -163,6 +163,37 @@ static String formatDuration(long ms) {
         return String.format("%02d:%02d:%02d", totalSeconds / 3600, (totalSeconds % 3600) / 60, totalSeconds % 60);
     }
 
+    /**
+     * Pass-rate and duration of the last {@code maxRuns} runs from the metrics history, oldest
+     * first, as a JSON array for the trend charts. Empty array when there is no history.
+     */
+    static String buildTrendData(int maxRuns) {
+        File dir = ReportPaths.metricsHistoryDir();
+        File[] files = dir.isDirectory() ? dir.listFiles((d, n) -> n.endsWith(".json")) : null;
+        if (files == null || files.length == 0) return "[]";
+        java.util.Arrays.sort(files, java.util.Comparator.comparing(File::getName));
+        int from = Math.max(0, files.length - maxRuns);
+        ObjectMapper mapper = new ObjectMapper();
+        com.fasterxml.jackson.databind.node.ArrayNode out = mapper.createArrayNode();
+        for (int i = from; i < files.length; i++) {
+            try {
+                JsonNode n = mapper.readTree(files[i]);
+                com.fasterxml.jackson.databind.node.ObjectNode run = out.addObject();
+                String name = files[i].getName().replaceAll("^.*metrics-|\\.json$", "");
+                run.put("label", name.length() >= 13
+                        ? name.substring(4, 6) + "-" + name.substring(6, 8) + " " + name.substring(9, 11) + ":" + name.substring(11, 13)
+                        : name);
+                run.put("passRate", n.path("passRate").asDouble(0));
+                run.put("failed", n.path("failedTests").asInt(0));
+                long ms = n.path("suiteDurationMs").asLong(0);
+                run.put("durationSec", Math.round((ms > 0 ? ms : n.path("totalTimeMs").asLong(0)) / 100.0) / 10.0);
+            } catch (Exception ignored) {
+                // unreadable history file: skip it
+            }
+        }
+        return out.toString();
+    }
+
     static String buildHtml(JsonNode root) {
 
         String executionPercentiles =
@@ -264,6 +295,7 @@ static String buildHtml(JsonNode root) {
                 .replace("{{SLOWEST_TESTS}}", slowestSection)
                 .replace("{{FLAKINESS_SECTION}}", flakinessSection)
                 .replace("{{DONUT_DATA}}", donutData)
+                .replace("{{TREND_DATA}}", buildTrendData(20))
                 .replace("{{ROWS}}", rows.toString())
                 .replace("{{FAILURE_ROWS}}", failureRows)
                 .replace("{{FAILURE_GROUPS}}", failureGroups)

src/main/resources/report-template.html

@@ -427,6 +427,18 @@ <h1>Selenium Boot Report</h1>
                 </div>
             </div>
 
+            <!-- Trend over runs (hidden until there are 2+ runs of history) -->
+            <div class="charts-row" id="trendRow" style="display:none">
+                <div class="card chart-card">
+                    <div class="card-header">Pass Rate Trend (%)</div>
+                    <div class="card-body"><canvas id="trendRateChart"></canvas></div>
+                </div>
+                <div class="card chart-card">
+                    <div class="card-header">Suite Duration Trend (s)</div>
+                    <div class="card-body"><canvas id="trendTimeChart"></canvas></div>
+                </div>
+            </div>
+
             <!-- Retry summary -->
             {{RETRY_SECTION}}
 
@@ -585,6 +597,23 @@ <h1>Selenium Boot Report</h1>
     });
 }
 
+// ── Trend over runs ──
+const trendData = {{TREND_DATA}};
+if (window.Chart && trendData.length >= 2) {
+    document.getElementById('trendRow').style.display = '';
+    const labels = trendData.map(r => r.label);
+    const line = (el, label, data, color, max) => new Chart(document.getElementById(el), {
+        type: 'line',
+        data: { labels, datasets: [{ label, data, borderColor: color, backgroundColor: color + '33',
+            fill: true, tension: .3, pointRadius: 3 }] },
+        options: { responsive: true, maintainAspectRatio: false,
+            plugins: { legend: { display: false } },
+            scales: { x: { grid: { display: false } }, y: { beginAtZero: true, max } } }
+    });
+    line('trendRateChart', 'Pass rate (%)', trendData.map(r => r.passRate), '#43a047', 100);
+    line('trendTimeChart', 'Duration (s)', trendData.map(r => r.durationSec), '#303f9f');
+}
+
 // ── Collapse / expand class groups ──
 function toggleGroup(groupId) {
     const members = document.querySelectorAll(`.group-member[data-group="${groupId}"]`);

src/test/java/com/seleniumboot/reporting/HtmlReportGeneratorTest.java

@@ -101,4 +101,41 @@ public void reportShowsSuiteWallClockInHhMmSs() throws Exception {
         assertTrue(html.contains("<div class=\"stat-value\">01:01:01</div>"), "stat tile shows suite time");
         assertFalse(html.contains("Avg Time (ms)"), "per-test average tile is gone");
     }
+
+    @Test
+    public void trendData_isChronological_andLimitedToLastRuns() throws Exception {
+        java.nio.file.Path dir = java.nio.file.Files.createTempDirectory("sb-history");
+        System.setProperty("seleniumboot.history.dir", dir.toString());
+        try {
+            for (int i = 1; i <= 3; i++) {
+                java.nio.file.Files.writeString(dir.resolve("selenium-boot-metrics-2026101" + i + "-10300" + i + ".json"),
+                        "{\"passRate\":" + (i * 30) + ".0,\"failedTests\":" + i + ",\"suiteDurationMs\":" + (i * 2000) + "}");
+            }
+            java.nio.file.Files.writeString(dir.resolve("selenium-boot-metrics-20261019-103000.json"), "not json");
+
+            JsonNode trend = new ObjectMapper().readTree(HtmlReportGenerator.buildTrendData(2));
+            assertEquals(trend.size(), 1, "last 2 files taken, the unreadable one skipped");
+            assertEquals(trend.get(0).get("passRate").asDouble(), 90.0);
+            assertEquals(trend.get(0).get("durationSec").asDouble(), 6.0);
+            assertEquals(trend.get(0).get("label").asText(), "10-13 10:30");
+
+            JsonNode all = new ObjectMapper().readTree(HtmlReportGenerator.buildTrendData(20));
+            assertEquals(all.size(), 3);
+            assertEquals(all.get(0).get("passRate").asDouble(), 30.0, "oldest first");
+        } finally {
+            System.clearProperty("seleniumboot.history.dir");
+        }
+    }
+
+    @Test
+    public void trendData_emptyWithoutHistory() throws Exception {
+        System.setProperty("seleniumboot.history.dir",
+                java.nio.file.Files.createTempDirectory("sb-empty").toString());
+        try {
+            assertEquals(HtmlReportGenerator.buildTrendData(20), "[]");
+            assertTrue(html(1, 0).contains("const trendData = [];"));
+        } finally {
+            System.clearProperty("seleniumboot.history.dir");
+        }
+    }
 }