Minecraft snapshot 25w03a introduces test blocks which can be placed within the structure templates representing a game test. However, the various messages and behavior surrounding these blocks are inconsistent regarding whether multiple can be placed within a structure.

The changelog mentions the following:

• start: Triggers a redstone pulse when the test starts
• log: Logs a message to the log file when powered by redstone
• fail: Fails the test when powered by redstone
• accept: Completes the test when powered by redstone

Block-based tests are required to have at least one start block and one accept block in the structure.

The test block interface considers accept mode to 'Accept success for (part of) a test' and start mode to be 'The starting point for a test'. These descriptions imply that accept mode would be allowed in multiple blocks and that start mode would always be a single block.

When running tests, start and accept modes must have exactly one test block in the structure template. Log and fail modes have no restriction on the count.

In summary: