diff -r 000000000000 -r 6474c204b198 toolkit/devtools/server/tests/unit/test_objectgrips-12.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/toolkit/devtools/server/tests/unit/test_objectgrips-12.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,145 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// Test getDisplayString.
+
+var gDebuggee;
+var gClient;
+var gThreadClient;
+
+function run_test()
+{
+  initTestDebuggerServer();
+  gDebuggee = addTestGlobal("test-grips");
+  gDebuggee.eval(function stopMe(arg1) {
+    debugger;
+  }.toString());
+
+  gClient = new DebuggerClient(DebuggerServer.connectPipe());
+  gClient.connect(function() {
+    attachTestTabAndResume(gClient, "test-grips", function(aResponse, aTabClient, aThreadClient) {
+      gThreadClient = aThreadClient;
+      test_display_string();
+    });
+  });
+  do_test_pending();
+}
+
+function test_display_string()
+{
+  const testCases = [
+    {
+      input: "new Boolean(true)",
+      output: "true"
+    },
+    {
+      input: "new Number(5)",
+      output: "5"
+    },
+    {
+      input: "new String('foo')",
+      output: "foo"
+    },
+    {
+      input: "new Map()",
+      output: "[object Map]"
+    },
+    {
+      input: "[,,,,,,,]",
+      output: ",,,,,,"
+    },
+    {
+      input: "[1, 2, 3]",
+      output: "1,2,3"
+    },
+    {
+      input: "[undefined, null, true, 'foo', 5]",
+      output: ",,true,foo,5"
+    },
+    {
+      input: "[{},{}]",
+      output: "[object Object],[object Object]"
+    },
+    {
+      input: "(" + function() {
+        const arr = [1];
+        arr.push(arr);
+        return arr;
+      } + ")()",
+      output: "1,"
+    },
+    {
+      input: "{}",
+      output: "[object Object]"
+    },
+    {
+      input: "Object.create(null)",
+      output: "[object Object]"
+    },
+    {
+      input: "new Error('foo')",
+      output: "Error: foo"
+    },
+    {
+      input: "new SyntaxError()",
+      output: "SyntaxError"
+    },
+    {
+      input: "new ReferenceError('')",
+      output: "ReferenceError"
+    },
+    {
+      input: "(" + function() {
+        const err = new Error("bar");
+        err.name = "foo";
+        return err;
+      } + ")()",
+      output: "foo: bar"
+    },
+    {
+      input: "() => {}",
+      output: "() => {}"
+    },
+    {
+      input: "function (foo, bar) {}",
+      output: "function (foo, bar) {}"
+    },
+    {
+      input: "function foo(bar) {}",
+      output: "function foo(bar) {}"
+    },
+    {
+      input: "Array",
+      output: Array + ""
+    },
+    {
+      input: "/foo[bar]/g",
+      output: "/foo[bar]/g"
+    },
+    {
+      input: "new Proxy({}, {})",
+      output: "[object Object]"
+    }
+  ];
+
+  gThreadClient.addOneTimeListener("paused", function(aEvent, aPacket) {
+    const args = aPacket.frame.arguments;
+
+    (function loop() {
+      const objClient = gThreadClient.pauseGrip(args.pop());
+      objClient.getDisplayString(function({ displayString }) {
+        do_check_eq(displayString, testCases.pop().output);
+        if (args.length) {
+          loop();
+        } else {
+          gThreadClient.resume(function() {
+            finishClient(gClient);
+          });
+        }
+      });
+    })();
+  });
+
+  const inputs = testCases.map(({ input }) => input).join(",");
+  gDebuggee.eval("stopMe(" + inputs + ")");
+}