1 files changed, 40 insertions, 0 deletions
diff --git a/services/common/tests/unit/test_async_chain.js b/services/common/tests/unit/test_async_chain.js
new file mode 100644
index 0000000000..3277c92f81
--- /dev/null
+++ b/services/common/tests/unit/test_async_chain.js
@@ -0,0 +1,40 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+const { Async } = ChromeUtils.importESModule(
+  "resource://services-common/async.sys.mjs"
+);
+
+function run_test() {
+  _("Chain a few async methods, making sure the 'this' object is correct.");
+
+  let methods = {
+    save(x, callback) {
+      this.x = x;
+      callback(x);
+    },
+    addX(x, callback) {
+      callback(x + this.x);
+    },
+    double(x, callback) {
+      callback(x * 2);
+    },
+    neg(x, callback) {
+      callback(-x);
+    },
+  };
+  methods.chain = Async.chain;
+
+  // ((1 + 1 + 1) * (-1) + 1) * 2 + 1 = -3
+  methods.chain(
+    methods.save,
+    methods.addX,
+    methods.addX,
+    methods.neg,
+    methods.addX,
+    methods.double,
+    methods.addX,
+    methods.save
+  )(1);
+  Assert.equal(methods.x, -3);
+}