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Systems for issue tracking may be both integrated and standalone. Examples are github and gitlab (integrated), Jira from Atlasssian (standalone, but integrated with other Atlassian products), bugzilla (standalone), ...
There is also a process of using strict issue tracking where code updates must be associated with an issue, code is updated if and only if there is a specified issue.
Code review
When providing code for an issue, you often want to review it before allowing the code to be committed into and merged with the code repository. This is particularly relevant when code is contributed from outsiders, like in open source projects, but also relevant in more closed settings, to ensure quality. Sometimes you also want to run CI on the code, before doing the review and stamp of approval.
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