--- a/devtools/shared/webconsole/test/common.js
+++ b/devtools/shared/webconsole/test/common.js
@@ -3,17 +3,17 @@
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
 "use strict";
 
 /* exported ObjectClient, attachConsole, attachConsoleToTab, attachConsoleToWorker,
    closeDebugger, checkConsoleAPICalls, checkRawHeaders, runTests, nextTest, Ci, Cc,
-   withActiveServiceWorker, Services */
+   withActiveServiceWorker, Services, consoleAPICall */
 
 const {require} = ChromeUtils.import("resource://devtools/shared/Loader.jsm", {});
 const {DebuggerServer} = require("devtools/server/main");
 const {DebuggerClient} = require("devtools/shared/client/debugger-client");
 const ObjectClient = require("devtools/shared/client/object-client");
 const Services = require("Services");
 
 function initCommon() {
@@ -124,19 +124,25 @@ var _attachConsole = async function(
   } else {
     state.actor = tab.consoleActor;
     state.dbgClient.attachConsole(tab.consoleActor, listeners,
                                    _onAttachConsole.bind(null, state));
   }
 };
 
 function closeDebugger(state, callback) {
-  state.dbgClient.close().then(callback);
+  const onClose = state.dbgClient.close();
+
   state.dbgClient = null;
   state.client = null;
+
+  if (typeof callback === "function") {
+    onClose.then(callback);
+  }
+  return onClose;
 }
 
 function checkConsoleAPICalls(consoleCalls, expectedConsoleCalls) {
   is(consoleCalls.length, expectedConsoleCalls.length,
     "received correct number of console calls");
   expectedConsoleCalls.forEach(function(message, index) {
     info("checking received console call #" + index);
     checkConsoleAPICall(consoleCalls[index], expectedConsoleCalls[index]);
@@ -259,8 +265,22 @@ function withActiveServiceWorker(win, ur
         if (sw.state === "activated") {
           sw.removeEventListener("statechange", stateHandler);
           resolve(swr);
         }
       });
     });
   });
 }
+
+/**
+ *
+ * @param {DebuggerClient} debuggerClient
+ * @param {Function} consoleCall: A function which calls the consoleAPI, e.g. :
+ *                         `() => top.console.log("test")`.
+ * @returns {Promise} A promise that will be resolved with the packet sent by the server
+ *                    in response to the consoleAPI call.
+ */
+function consoleAPICall(debuggerClient, consoleCall) {
+  const onConsoleAPICall = debuggerClient.addOneTimeListener("consoleAPICall");
+  consoleCall();
+  return onConsoleAPICall;
+}

--- a/devtools/shared/webconsole/test/test_console_assert.html
+++ b/devtools/shared/webconsole/test/test_console_assert.html
@@ -14,79 +14,84 @@ window.onload = async function () {
   SimpleTest.waitForExplicitFinish();
   let state;
   try {
     state = await new Promise(resolve =>
       attachConsole(["ConsoleAPI"], resolve)
     );
     const {dbgClient} = state;
 
-    const consoleAPICall = consoleCall => {
-      const onConsoleAPICall = dbgClient.addOneTimeListener("consoleAPICall");
-      consoleCall();
-      return onConsoleAPICall;
-    };
-
-    await testFalseAssert(consoleAPICall);
-    await testFalsyAssert(consoleAPICall);
-    await testUndefinedAssert(consoleAPICall);
-    await testNullAssert(consoleAPICall);
-    await testTrueAssert(consoleAPICall);
+    await testFalseAssert(dbgClient);
+    await testFalsyAssert(dbgClient);
+    await testUndefinedAssert(dbgClient);
+    await testNullAssert(dbgClient);
+    await testTrueAssert(dbgClient);
 
   } catch (e) {
     ok(false, `Error thrown: ${e.message}`);
   }
 
-  closeDebugger(state, () => SimpleTest.finish());
+  await closeDebugger(state);
+  SimpleTest.finish();
 };
 
-async function testFalseAssert(consoleAPICall) {
+async function testFalseAssert(debuggerClient) {
   info(`Testing console.assert(false)`);
-  const packet = await consoleAPICall(() =>
-    top.console.assert(false, "assertion is false"));
+  const packet = await consoleAPICall(
+    debuggerClient,
+    () => top.console.assert(false, "assertion is false")
+  );
 
   checkConsoleAPICall(packet.message, {
     arguments: ["assertion is false"]
   });
 }
 
-async function testFalsyAssert(consoleAPICall) {
+async function testFalsyAssert(debuggerClient) {
   info(`Testing console.assert(0")`);
-  const packet = await consoleAPICall(() =>
-    top.console.assert(0, "assertion is false"));
+  const packet = await consoleAPICall(
+    debuggerClient,
+    () => top.console.assert(0, "assertion is false")
+  );
 
   checkConsoleAPICall(packet.message, {
     arguments: ["assertion is false"]
   });
 }
 
-async function testUndefinedAssert(consoleAPICall) {
+async function testUndefinedAssert(debuggerClient) {
   info(`Testing console.assert(undefined)`);
-  const packet = await consoleAPICall(() =>
-    top.console.assert(undefined, "assertion is false"));
+  const packet = await consoleAPICall(
+    debuggerClient,
+    () => top.console.assert(undefined, "assertion is false")
+  );
 
   checkConsoleAPICall(packet.message, {
     arguments: ["assertion is false"]
   });
 }
 
-async function testNullAssert(consoleAPICall) {
+async function testNullAssert(debuggerClient) {
   info(`Testing console.assert(null)`);
-  const packet = await consoleAPICall(() =>
-    top.console.assert(null, "assertion is false"));
+  const packet = await consoleAPICall(
+    debuggerClient,
+    () => top.console.assert(null, "assertion is false")
+  );
 
   checkConsoleAPICall(packet.message, {
     arguments: ["assertion is false"]
   });
 }
 
-async function testTrueAssert(consoleAPICall) {
+async function testTrueAssert(debuggerClient) {
   info(`Testing console.assert(true)`);
-  const onConsoleApiCall = consoleAPICall(() =>
-    top.console.assert(true, "assertion is false"));
+  const onConsoleApiCall = consoleAPICall(
+    debuggerClient,
+    () => top.console.assert(true, "assertion is false")
+  );
 
   const TIMEOUT = Symbol();
   const onTimeout = new Promise(resolve => setTimeout(() => resolve(TIMEOUT), 1000));
 
   const res = await Promise.race([onConsoleApiCall, onTimeout]);
   is(res, TIMEOUT,
     "There was no consoleAPICall event in response to a truthy console.assert");
 }

--- a/devtools/shared/webconsole/test/test_console_group_styling.html
+++ b/devtools/shared/webconsole/test/test_console_group_styling.html
@@ -28,17 +28,18 @@ window.onload = async function () {
     await testMultipleCustomStyleGroup(debuggerClient);
     await testMultipleCustomStyleGroupCollapsed(debuggerClient);
     await testFormatterWithNoStyleGroup(debuggerClient);
     await testFormatterWithNoStyleGroupCollapsed(debuggerClient);
   } catch (e) {
     ok(false, `Error thrown: ${e.message}`);
   }
 
-  closeDebugger(state, () => SimpleTest.finish());
+  await closeDebugger(state);
+  SimpleTest.finish();
 };
 
 async function testSingleCustomStyleGroup(debuggerClient) {
   info("Testing console.group with a custom style");
   let packet = await consoleAPICall(
     debuggerClient,
     () => top.console.group("%cfoobar", "color:red")
   );
@@ -109,22 +110,16 @@ async function testFormatterWithNoStyleG
   );
 
   checkConsoleAPICall(packet.message, {
     arguments: ["%cfoobaz"],
     styles: []
   });
 }
 
-function consoleAPICall(debuggerClient, consoleCall) {
-  const onConsoleAPICall = debuggerClient.addOneTimeListener("consoleAPICall");
-  consoleCall();
-  return onConsoleAPICall;
-}
-
   </script>
 </head>
 <body>
   <p id="display"></p>
   <div id="content" style="display: none">
   </div>
   <pre id="test">
   </pre>

--- a/devtools/shared/webconsole/test/test_console_timestamp.html
+++ b/devtools/shared/webconsole/test/test_console_timestamp.html
@@ -37,23 +37,16 @@ window.onload = async function () {
   } catch (e) {
     ok(false, `Error thrown: ${e.message}`);
   }
 
   await closeDebugger(state);
   SimpleTest.finish();
 };
 
-
-function consoleAPICall(debuggerClient, consoleCall) {
-  const onConsoleAPICall = debuggerClient.addOneTimeListener("consoleAPICall");
-  consoleCall();
-  return onConsoleAPICall;
-}
-
   </script>
 </head>
 <body>
   <p id="display"></p>
   <div id="content" style="display: none">
   </div>
   <pre id="test">
   </pre>