diff --git a/tests/testthat/test-renderer-grade-trends.R b/tests/testthat/test-renderer-grade-trends.R
new file mode 100644
index 000000000..ff929f738
--- /dev/null
+++ b/tests/testthat/test-renderer-grade-trends.R
@@ -0,0 +1,161 @@
+library(XML)
+library(animint2)
+
+acontext("student performance subject comparison")
+
+subject_summary <- data.frame(
+    subject = rep(c(
+        "Mathematics", "Physics", "Chemistry",
+        "Biology", "English", "History"
+    ), times = 2),
+    mean_grade = c(
+        72.5, 74.3, 75.8, 77.2, 79.1, 80.4,
+        73.5, 75.3, 76.8, 78.2, 80.1, 81.4
+    ),
+    semester = rep(c("Sem1", "Sem2"), each = 6),
+    stringsAsFactors = FALSE
+)
+
+student_points <- data.frame(
+    subject = rep(c(
+        "Mathematics", "Physics", "Chemistry",
+        "Biology", "English", "History"
+    ), each = 5),
+    grade = c(
+        65, 70, 72, 75, 80,
+        68, 72, 74, 76, 82,
+        70, 73, 75, 78, 83,
+        72, 75, 77, 80, 85,
+        74, 77, 79, 82, 87,
+        75, 78, 80, 83, 88
+    ),
+    semester = rep("Sem1", 30),
+    stringsAsFactors = FALSE
+)
+
+viz <- animint(
+    subjectComparison = ggplot() +
+        theme_bw() +
+        theme_animint(width = 680, height = 380) +
+        geom_bar(
+            aes(
+                x = subject, y = mean_grade,
+                fill = subject, key = subject
+            ),
+            showSelected = "semester",
+            clickSelects = "subject",
+            data = subject_summary,
+            stat = "identity",
+            position = "identity",
+            alpha = 0.7
+        ) +
+        geom_point(
+            aes(
+                x = subject, y = grade,
+                color = subject,
+                key = paste(subject, grade)
+            ),
+            showSelected = "semester",
+            clickSelects = "subject",
+            data = student_points,
+            alpha = 0.6
+        ) +
+        ggtitle("Subject Performance Comparison") +
+        xlab("Subject") +
+        ylab("Grade (%)"),
+    first = list(semester = "Sem1", subject = "Mathematics")
+)
+
+info <- animint2HTML(viz)
+
+# test 1 - exactly 6 bar rects rendered, one per subject
+test_that("subjectComparison renders exactly 6 bar rects for 6 subjects", {
+    rects <- getNodeSet(
+        info$html,
+        "//rect[not(@class)]"
+    )
+    expect_equal(length(rects), 6L)
+})
+
+# test 2 - point circles rendered for student grades
+test_that("subjectComparison renders point circles for students", {
+    circles <- getNodeSet(
+        info$html,
+        '//g[contains(@class,"geom")]//circle'
+    )
+    expect_true(length(circles) > 0)
+})
+
+# test 3 - selector widget exists for subject
+test_that("subject selector widget is present", {
+    inputs <- getNodeSet(
+        info$html,
+        "//select | //input[@type='radio']"
+    )
+    expect_true(length(inputs) > 0)
+})
+
+# test 4 - semester selector has exactly 2 options (Sem1 and Sem2)
+test_that("semester selector has exactly 2 options", {
+    options <- getNodeSet(
+        info$html,
+        "//select//option"
+    )
+    expect_equal(length(options), 2L)
+})
+
+# test 5 - plot title is rendered correctly in SVG (fixed: more specific)
+test_that("plot title text is rendered exactly once in SVG", {
+    titles <- getNodeSet(
+        info$html,
+        '//text[contains(text(), "Subject Performance Comparison")]'
+    )
+    expect_equal(length(titles), 1L)
+})
+
+# test 6 - all 6 subject names appear as axis tick labels
+test_that("all 6 subject names appear as x axis labels", {
+    subjects <- c(
+        "Mathematics", "Physics", "Chemistry",
+        "Biology", "English", "History"
+    )
+    tick_nodes <- getNodeSet(
+        info$html,
+        "//g[contains(@class,'xaxis')]//text"
+    )
+    tick_labels <- sapply(tick_nodes, xmlValue)
+    for (s in subjects) {
+        expect_true(
+            any(grepl(s, tick_labels)),
+            info = paste("subject not found in axis labels:", s)
+        )
+    }
+})
+
+# test 7 - clicking Physics legend highlights Physics bar
+test_that("clicking Physics legend toggles Physics selection", {
+    # before - only Mathematics selected
+    html_before <- getHTML()
+    math_label <- getNodeSet(
+        html_before,
+        '//td[@id="plot_subjectComparison_subject_variable_Mathematics_label"]'
+    )
+    before_opacity <- xmlGetAttr(math_label[[1]], "style")
+    
+    # click Physics to add it to selection
+    clickID("plot_subjectComparison_subject_variable_Physics")
+    Sys.sleep(1)
+    
+    # after - Physics label should now be full opacity
+    html_after <- getHTML()
+    physics_label <- getNodeSet(
+        html_after,
+        '//td[@id="plot_subjectComparison_subject_variable_Physics_label"]'
+    )
+    after_opacity <- xmlGetAttr(physics_label[[1]], "style")
+    
+    # Physics opacity changes from 0.5 to 1 after click
+    expect_true(grepl("opacity: 1", after_opacity))
+})
+
+