A test log records the output of a test during its execution including any text that was written to console output streams, exceptions that occurred, and anything else the test writer might want to save.

A log consists of zero or more log streams that are opened automatically on demand to capture independent sequences of log output. Each stream can further be broken down into possibly nested sections to classify output during different phases of test execution (useful for drilling into complex tests). In addition to text, a log can contain attachments that are either attached at the top level of the log or embedded into log streams. Attachments are typed by mime-type and can contain Text, Xml, Images, Blobs, or any other content. Certain test frameworks may automatically create attachments to gather all manner of diagnostic information over the course of the test.

Test log messages are not echoed to the console or runtime log during test execution, they are incorporated into the test report. Use DiagnosticLog instead if you wish to write messages immediately where the operator can see them.