If you're a user of the SwiftMailer package in your application, you may have hit on issues with your unit tests with mocking the library to isolate it from the actual email sending. Joe Ferguson is here to help with some advice in his latest post on mocking the library and how he used it to solve a problem in his own code.

A few days ago an issue came across my Jira queue that mentioned odd characters showing up in the subject line of our notification system. We use SwiftMailer library which is a fantastic library for sending mail.

[...] Something was taking our twig template that we use for our email subject and changing the encoding. This is normally done when you want to convert special characters so they’re not interpreted as code blocks. The example above is showing where an apostrophe is converted to “'”, the ASCII code equivalent.

He breaks the rest of the post into 3 steps (well, really 4 but there's a 2.5 in there) that he followed to mock the library out appropriately and be able to test the message sending without actually having to send. Code examples are included of both the code doing the sending and the test doing the mocking and verifying the subject lines on their emails (the original bug reported).