# `mix affected.files`
[🔗](https://github.com/mnox/mix_affected/blob/v0.1.0/lib/mix/tasks/affected.files.ex#L1)

Prints the test files a change set may affect. Run with `MIX_ENV=test`.

    mix affected.files --base origin/main
    git diff --name-only origin/main... | mix affected.files --files -
    mix affected.files --files changed.txt --format json --output selection.json

Input, exactly one of:

  * `--base <git-ref>` - files changed on `<ref>...HEAD`, plus uncommitted
    and untracked files (needs `.git`)
  * `--files <path|->` - newline-separated project-relative paths; `-`
    reads stdin

Options:

  * `--format text|json` - text (default) prints one test file per line; on
    a full run it prints nothing and the reason goes to stderr
  * `--explain` - the chain `changed file -> ... -> test` per selected test
    (text: one chain per line; JSON: the `explain` object)
  * `--output <path>` - write to a file instead of stdout
  * `--map <path>` - the test map to use; built there when missing
    (default `_build/test/mix_affected/test_map.etf`)

Exit status: 0 on any answer (including a full run and an empty
selection), 1 on a usage error, 2 when the graph or test map could not be
built (the output then says `full_run: true`).

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*Consult [api-reference.md](api-reference.md) for complete listing*