3.8 Quality Assurance

Monotone was constructed to serve both as a version control tool and as a quality assurance tool. The quality assurance features permit users to ignore, or “filter out”, versions which do not meet their criteria for quality. This section describes the way monotone represents and reasons about quality information.

Monotone often views the collection of revisions as a directed graph, in which revisions are the nodes and changes between revisions are the edges. We call this the revision graph. The revision graph has a number of important subgraphs, many of which overlap. For example, each branch is a subgraph of the revision graph, containing only the nodes carrying a particular branch cert.

Many of monotone’s operations involve searching the revision graph for the ancestors or descendants of a particular revision, or extracting the “heads” of a subgraph, which is the subgraph’s set of nodes with no descendants. For example, when you run the update command, monotone searches the subgraph consisting of descendants of the base revision of the current workspace, trying to locate a unique head to update the base revision to.

Monotone’s quality assurance mechanisms are mostly based on restricting the subgraph each command operates on. There are two methods used to restrict the subgraph:

• By restricting the set of trusted branch certificates, you can require that specific code reviewers have approved of each edge in the subgraph you focus on.
• By restricting the set of trusted testresult certificates, you can require that the endpoints of an update operation have a certificate asserting that the revision in question passed a certain test, or testsuite.

The evaluation of trust is done on a cert-by-cert basis by calling the Lua hook get_revision_cert_trust. This hook is only called when a cert has at least one good signature from a known key, and are passed all the keys which have signed the cert, as well as the cert’s ID, name and value. The hook can then evaluate the set of signers, as a group, and decide whether to grant or deny trust to the assertion made by the cert.

The evaluation of testresults is controlled by the accept_testresult_change hook (see accept_testresult_change). This hook is called when selecting update candidates, and is passed a pair of tables describing the testresult certs present on the source and proposed destination of an update. Only if the change in test results are deemed “acceptable” does monotone actually select an update target to merge into your workspace.