1 files changed, 24 insertions, 0 deletions
diff --git a/devtools/client/responsive/test/xpcshell/test_add_viewport.js b/devtools/client/responsive/test/xpcshell/test_add_viewport.js
new file mode 100644
index 0000000000..c9a6d9500b
--- /dev/null
+++ b/devtools/client/responsive/test/xpcshell/test_add_viewport.js
@@ -0,0 +1,24 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// Test adding viewports to the page.
+
+const {
+  addViewport,
+} = require("resource://devtools/client/responsive/actions/viewports.js");
+
+add_task(async function () {
+  const store = Store();
+  const { getState, dispatch } = store;
+
+  equal(getState().viewports.length, 0, "Defaults to no viewpots at startup");
+
+  dispatch(addViewport());
+  equal(getState().viewports.length, 1, "One viewport total");
+
+  // For the moment, there can be at most one viewport.
+  dispatch(addViewport());
+  equal(getState().viewports.length, 1, "One viewport total, again");
+});