Bug 1336124 - Add assert.session for checking if session is active; r=maja_zf

MozReview-Commit-ID: CmHFag2q1V2

--HG--
extra : rebase_source : 526e01466ce4a00a091dd88cb060d166c6ac4245

testing/marionette/assert.js

@@ -21,6 +21,26 @@ const isFirefox = () => Services.appinfo.name == "Firefox";
 /** Shorthands for common assertions made in Marionette. */
 this.assert = {};
 
+/**
+ * Asserts that Marionette has a session.
+ *
+ * @param {GeckoDriver} driver
+ *     Marionette driver instance.
+ * @param {string=} msg
+ *     Custom error message.
+ *
+ * @return {string}
+ *     Session ID.
+ *
+ * @throws {InvalidSessionIdError}
+ *     If |driver| does not have a session ID.
+ */
+assert.session = function (driver, msg = "") {
+  assert.that(sessionID => sessionID,
+      msg, InvalidSessionIdError)(driver.sessionId);
+  return driver.sessionId;
+};
+
 /**
  * Asserts that the current browser is Firefox Desktop.
  *

testing/marionette/test_assert.js

@@ -9,6 +9,15 @@ const {utils: Cu} = Components;
 Cu.import("chrome://marionette/content/assert.js");
 Cu.import("chrome://marionette/content/error.js");
 
+add_test(function test_session() {
+  assert.session({sessionId: "foo"});
+  for (let typ of [null, undefined, ""]) {
+    Assert.throws(() => assert.session({sessionId: typ}), InvalidSessionIdError);
+  }
+
+  run_next_test();
+});
+
 add_test(function test_platforms() {
   // at least one will fail
   let raised;