diff --git a/testing/web-platform/tests/mathml/relations/html5-tree/display-2-ref.html b/testing/web-platform/tests/mathml/relations/html5-tree/display-2-ref.html
new file mode 100644
index 000000000000..7864c0409914
--- /dev/null
+++ b/testing/web-platform/tests/mathml/relations/html5-tree/display-2-ref.html
@@ -0,0 +1,31 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8"/>
+<title>display attribute VS legacy mode attribute (reference)</title>
+</head>
+<body>
+  <p>Test passes if you see four green squares, the last one
+    centered and the others left-aligned.</p>
+  <p>
+    <math>
+      <mspace width="100px" height="100px" style="background: green"></mspace>
+    </math>
+  </p>
+  <p>
+    <math>
+      <mspace width="100px" height="100px" style="background: green"></mspace>
+    </math>
+  </p>
+  <p>
+    <math display="inline">
+      <mspace width="100px" height="100px" style="background: green"></mspace>
+    </math>
+  </p>
+  <p>
+    <math display="block">
+      <mspace width="100px" height="100px" style="background: green"></mspace>
+    </math>
+  </p>
+</body>
+</html>
diff --git a/testing/web-platform/tests/mathml/relations/html5-tree/display-2.html b/testing/web-platform/tests/mathml/relations/html5-tree/display-2.html
new file mode 100644
index 000000000000..d1c68e57c6ed
--- /dev/null
+++ b/testing/web-platform/tests/mathml/relations/html5-tree/display-2.html
@@ -0,0 +1,37 @@
+<!DOCTYPE html>
+<html>
+<head>
+<meta charset="utf-8"/>
+<title>display attribute VS legacy mode attribute</title>
+<link rel="help" href="https://mathml-refresh.github.io/mathml-core/#the-top-level-math-element">
+<link rel="help" href="https://www.w3.org/TR/MathML3/chapter2.html#id.2.2.2">
+<link rel="match" href="display-2-ref.html"/>
+<meta name="assert" content="Verify that the legacy mode attribute has no effect.">
+</head>
+<body>
+  <p>Test passes if you see four green squares, the last one
+    centered and the others left-aligned.</p>
+  <p>
+    <math mode="inline">
+      <mspace width="100px" height="100px" style="background: green"></mspace>
+    </math>
+  </p>
+  <p>
+    <math mode="display">
+      <mspace width="100px" height="100px" style="background: green"></mspace>
+    </math>
+  </p>
+  <p>
+    <math display="inline" mode="display">
+      <mspace width="100px" height="100px" style="background: green"></mspace>
+    </math>
+  </p>
+  <p>
+    <math display="block" mode="inline">
+      <mspace width="100px" height="100px" style="background: green"></mspace>
+    </math>
+  </p>
+  <script src="/mathml/support/feature-detection.js"></script>
+  <script>MathMLFeatureDetection.ensure_for_match_reftest("has_mspace");</script>
+</body>
+</html>
