diff --git a/README.md b/README.md
index 39c9abbaf..ecc037190 100644
--- a/README.md
+++ b/README.md
@@ -15,3 +15,23 @@ Step-up Middleware
 ## Installation
 
 Clone the repository or download the archive to a directory. Install the dependencies by running `composer install` and fill out the database credentials et cetera.
+
+## Notes
+
+### Mocking Broadway DateTime::now()
+
+To help with mocking time, the helper `BroadwayFixedDateTimeNow` was created. Call `::enable(DateTime)` to set a fixed
+date/time, and call `::disable()` to… disable it. It is recommended to run a tests in a separate process (see
+`IdentityCommandHandlerTest::testAYubikeyPossessionCanBeProven()`) when using this helper so the mock doesn't persist
+between tests.
+
+```php
+/** @runTestInSeparateProcess */
+public function testItWorks()
+{
+    # Trick `DateTime::now()` into thinking it is 1970.
+    BroadwayFixedDateTimeNow::enable(new \DateTime('@0'));
+
+    $this->assertEquals('1970-01-01T00:00:00.000000+00:00', \Broadway\Domain\DateTime::now()->toString());
+}
+```
diff --git a/composer.json b/composer.json
index c1931ae24..b3851abfb 100644
--- a/composer.json
+++ b/composer.json
@@ -9,7 +9,8 @@
         }
     },
     "autoload-dev": {
-        "classmap": ["src/Surfnet/StepupMiddleware/ApiBundle/Tests/Request/commands.php"]
+        "classmap": ["src/Surfnet/StepupMiddleware/ApiBundle/Tests/Request/commands.php"],
+        "files": ["src/Surfnet/StepupMiddleware/CommandHandlingBundle/Tests/microtime.php"]
     },
     "minimum-stability": "stable",
     "repositories": [{"type":"vcs","url":"https://github.com/rjkip/symfony"}],
diff --git a/composer.lock b/composer.lock
index 18a4a2989..d30e63d56 100644
--- a/composer.lock
+++ b/composer.lock
@@ -4,7 +4,7 @@
         "Read more about it at http://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file",
         "This file is @generated automatically"
     ],
-    "hash": "7d98cf9fdc16ef2615866095daaa8ff3",
+    "hash": "34a25fb58407cbf57d8912d9ed62196f",
     "packages": [
         {
             "name": "beberlei/assert",
diff --git a/src/Surfnet/StepupMiddleware/CommandHandlingBundle/Tests/BroadwayFixedDateTimeNow.php b/src/Surfnet/StepupMiddleware/CommandHandlingBundle/Tests/BroadwayFixedDateTimeNow.php
new file mode 100644
index 000000000..779b547b8
--- /dev/null
+++ b/src/Surfnet/StepupMiddleware/CommandHandlingBundle/Tests/BroadwayFixedDateTimeNow.php
@@ -0,0 +1,53 @@
+<?php
+
+/**
+ * Copyright 2014 SURFnet bv
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+namespace Surfnet\StepupMiddleware\CommandHandlingBundle\Tests;
+
+class BroadwayFixedDateTimeNow
+{
+    /**
+     * @var DateTime|null
+     */
+    private static $fixedReturnDateTime = null;
+
+    /**
+     * @param \DateTime $fixedReturnDateTime
+     */
+    public static function enable(\DateTime $fixedReturnDateTime)
+    {
+        self::$fixedReturnDateTime = $fixedReturnDateTime;
+    }
+
+    public static function disable()
+    {
+        self::$fixedReturnDateTime = null;
+    }
+
+    public static function microtime($getAsFloat)
+    {
+        if (self::$fixedReturnDateTime) {
+            if ($getAsFloat) {
+                return (float) self::$fixedReturnDateTime->format('U.u');
+            } else {
+                return self::$fixedReturnDateTime->format('0.u00 U');
+            }
+        } else {
+            return \microtime($getAsFloat);
+        }
+    }
+}
diff --git a/src/Surfnet/StepupMiddleware/CommandHandlingBundle/Tests/BroadwayFixedDateTimeNowTest.php b/src/Surfnet/StepupMiddleware/CommandHandlingBundle/Tests/BroadwayFixedDateTimeNowTest.php
new file mode 100644
index 000000000..f879e956f
--- /dev/null
+++ b/src/Surfnet/StepupMiddleware/CommandHandlingBundle/Tests/BroadwayFixedDateTimeNowTest.php
@@ -0,0 +1,59 @@
+<?php
+
+/**
+ * Copyright 2014 SURFnet bv
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+namespace Broadway\Domain;
+
+use Surfnet\StepupMiddleware\CommandHandlingBundle\Tests\BroadwayFixedDateTimeNow;
+
+/**
+ * @runTestsInSeparateProcesses
+ */
+class BroadwayFixedDateTimeNowTest extends \PHPUnit_Framework_TestCase
+{
+    public function testItMocksMicrotime()
+    {
+        BroadwayFixedDateTimeNow::enable(new \DateTime('@12345'));
+
+        $this->assertEquals(12345.0, microtime(true));
+        $this->assertEquals('0.00000000 12345', microtime());
+    }
+
+    public function testItWorksWithSeparateProcesses()
+    {
+        $this->assertInternalType('float', microtime(true));
+        $this->assertInternalType('string', microtime());
+    }
+
+    public function testItCanBeDisabledInTheSameProcess()
+    {
+        BroadwayFixedDateTimeNow::enable(new \DateTime('@12345'));
+        $this->assertEquals(12345.0, microtime(true));
+
+        BroadwayFixedDateTimeNow::disable();
+        $this->assertNotEquals(12345.0, microtime(true));
+        $this->assertInternalType('float', microtime(true));
+        $this->assertInternalType('string', microtime());
+    }
+
+    public function testWeAreVisiting1970()
+    {
+        BroadwayFixedDateTimeNow::enable(new \DateTime('@0'));
+
+        $this->assertEquals('1970-01-01T00:00:00.000000+00:00', DateTime::now()->toString());
+    }
+}
diff --git a/src/Surfnet/StepupMiddleware/CommandHandlingBundle/Tests/microtime.php b/src/Surfnet/StepupMiddleware/CommandHandlingBundle/Tests/microtime.php
new file mode 100644
index 000000000..c517e34ca
--- /dev/null
+++ b/src/Surfnet/StepupMiddleware/CommandHandlingBundle/Tests/microtime.php
@@ -0,0 +1,26 @@
+<?php
+
+/**
+ * Copyright 2014 SURFnet bv
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+namespace Broadway\Domain;
+
+use Surfnet\StepupMiddleware\CommandHandlingBundle\Tests\BroadwayFixedDateTimeNow;
+
+function microtime($getAsFloat = false)
+{
+    return BroadwayFixedDateTimeNow::microtime($getAsFloat);
+}