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diff --git a/testing/web-platform/tests/css/css-properties-values-api/animation/custom-property-animation-time-space-list.html b/testing/web-platform/tests/css/css-properties-values-api/animation/custom-property-animation-time-space-list.html
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+++ b/testing/web-platform/tests/css/css-properties-values-api/animation/custom-property-animation-time-space-list.html
@@ -0,0 +1,59 @@
+<!DOCTYPE html>
+<link rel="help" href="https://drafts.css-houdini.org/css-properties-values-api-1">
+<script src="/resources/testharness.js"></script>
+<script src="/resources/testharnessreport.js"></script>
+<script src="../resources/utils.js"></script>
+<div id="target"></div>
+<script>
+
+animation_test({
+  syntax: "<time>+",
+  inherits: false,
+  initialValue: "0s"
+}, {
+  keyframes: ["100s 150s", "200s 250s"],
+  expected: "150s 200s"
+}, 'Animating a custom property of type <time>+');
+
+animation_test({
+  syntax: "<time>+",
+  inherits: false,
+  initialValue: "100s 150s"
+}, {
+  keyframes: "200s 250s",
+  expected: "150s 200s"
+}, 'Animating a custom property of type <time>+ with a single keyframe');
+
+animation_test({
+  syntax: "<time>+",
+  inherits: false,
+  initialValue: "50s 100s"
+}, {
+  composite: "add",
+  keyframes: ["150s 200s", "250s 300s"],
+  expected: "250s 350s"
+}, 'Animating a custom property of type <time>+ with additivity');
+
+animation_test({
+  syntax: "<time>+",
+  inherits: false,
+  initialValue: "50s 100s"
+}, {
+  composite: "add",
+  keyframes: "150s 200s",
+  expected: "125s 200s"
+}, 'Animating a custom property of type <time>+ with a single keyframe and additivity');
+
+animation_test({
+  syntax: "<time>+",
+  inherits: false,
+  initialValue: "0s 0s"
+}, {
+  iterationComposite: "accumulate",
+  keyframes: ["0s 50s", "100s 100s"],
+  expected: "250s 275s"
+}, 'Animating a custom property of type <time>+ with iterationComposite');
+
+discrete_animation_test("<time>+", '10s 20s', '30s', 'Animating a custom property of type <time>+ with different lengths is discrete');
+
+</script>