Incoming Webhooks are a simple way to post messages from external sources into Slack. They make use of normal HTTP requests with a JSON payload that includes the message text and some options. Message Attachments can also be used in Incoming Webhooks to display richly-formatted messages that stand out from regular chat messages.
When I took my first real dev job in the late 90s, it was not common for developers to write their own automated tests. Instead, large companies depended on teams of testers, who tested manually, or were experts in complex (and expensive) automation software. Small companies were more likely to depend on code review, months of “integration” after the “development,”…or most commonly: pure hope.