Inspect the contents of log output during Java unit test (no mock used)

Overview

Inspect the contents of log output during unit test (no mock used)

environment

• Java
• slf4j 1.7.26
• logback 1.2.3

Method explanation

See Sample Code for the detailed method.

In theory,

• Add a new ʻAppender` to the root logger at the start of the test
• At this time, ʻoverride`` doAppend () of ʻAppender to be added, and ʻadd () ʻadd () the ʻILoggingEvent` received as an argument to the list of the external scope.
• Check ʻI Logging Event` in the List after the function you want to test is finished
• Detach the added ʻAppender` from the root logger

The flow.

Note that if you leave Appender added to the root logger and do not detach it, you will retain logging for all subsequent tests.

Digression

I wrote it on the assumption that it will be added to the root logger, but if you specify the logger in detail (like getLogger ("jp.co.hoge ")) and add ʻAppender` there, only that part will be logged. It is also possible.