# Writing tests Each Bats test file is evaluated _n+1_ times, where _n_ is the number of test cases in the file. The first run counts the number of test cases, then iterates over the test cases and executes each one in its own process. For more details about how Bats evaluates test files, see [Bats Evaluation Process][bats-eval] on the wiki. For sample test files, see [examples](https://github.com/bats-core/bats-core/tree/master/docs/examples). [bats-eval]: https://github.com/bats-core/bats-core/wiki/Bats-Evaluation-Process ## `run`: Test other commands Many Bats tests need to run a command and then make assertions about its exit status and output. Bats includes a `run` helper that invokes its arguments as a command, saves the exit status and output into special global variables, and then returns with a `0` status code so you can continue to make assertions in your test case. For example, let's say you're testing that the `foo` command, when passed a nonexistent filename, exits with a `1` status code and prints an error message. ```bash @test "invoking foo with a nonexistent file prints an error" { run foo nonexistent_filename [ "$status" -eq 1 ] [ "$output" = "foo: no such file 'nonexistent_filename'" ] } ``` The `$status` variable contains the status code of the command, and the `$output` variable contains the combined contents of the command's standard output and standard error streams. A third special variable, the `$lines` array, is available for easily accessing individual lines of output. For example, if you want to test that invoking `foo` without any arguments prints usage information on the first line: ```bash @test "invoking foo without arguments prints usage" { run foo [ "$status" -eq 1 ] [ "${lines[0]}" = "usage: foo " ] } ``` __Note:__ The `run` helper executes its argument(s) in a subshell, so if writing tests against environmental side-effects like a variable's value being changed, these changes will not persist after `run` completes. ### When not to use `run` In some cases, using `run` is redundant and results in a longer and less readable code. Here are a few examples. #### 1. In case you only need to check the command succeeded, it is better to not use run, since ```bash run command args ... echo "$output" [ "$status" -eq 0 ] ``` is equivalent to ```bash command args ... ``` since bats sets `set -e` for all tests. #### 2. In case you want to hide the command output (which `run` does), use output redirection instead This ```bash run command ... [ "$status" -eq 0 ] ``` is equivalent to ```bash command ... >/dev/null ``` Note that the output is only shown if the test case fails. #### 3. In case you need to assign command output to a variable (and maybe check the command exit status), it is better to not use run, since ```bash run command args ... [ "$status" -eq 0 ] var="$output" ``` is equivalent to ```bash var=$(command args ...) ``` #### Comment syntax External tools (like `shellcheck`, `shfmt`, and various IDE's) may not support the standard `.bats` syntax. Because of this, we provide a valid `bash` alterntative: ```bash function invoking_foo_without_arguments_prints_usage { #@test run foo [ "$status" -eq 1 ] [ "${lines[0]}" = "usage: foo " ] } ``` When using this syntax, the function name will be the title in the result output and the value checked when using `--filter`. ### `load`: Share common code You may want to share common code across multiple test files. Bats includes a convenient `load` command for sourcing a Bash source file relative to the location of the current test file. For example, if you have a Bats test in `test/foo.bats`, the command ```bash load test_helper.bash ``` will source the script `test/test_helper.bash` in your test file (limitations apply, see below). This can be useful for sharing functions to set up your environment or load fixtures. `load` delegates to Bash's `source` command after resolving relative paths. As pointed out by @iatrou in , using the `declare` builtin restricts scope of a variable. Thus, since actual `source`-ing is performed in context of the `load` function, `declare`d symbols will _not_ be made available to callers of `load`. > For backwards compatibility `load` first searches for a file ending in > `.bash` (e.g. `load test_helper` searches for `test_helper.bash` before > it looks for `test_helper`). This behaviour is deprecated and subject to > change, please use exact filenames instead. ### `skip`: Easily skip tests Tests can be skipped by using the `skip` command at the point in a test you wish to skip. ```bash @test "A test I don't want to execute for now" { skip run foo [ "$status" -eq 0 ] } ``` Optionally, you may include a reason for skipping: ```bash @test "A test I don't want to execute for now" { skip "This command will return zero soon, but not now" run foo [ "$status" -eq 0 ] } ``` Or you can skip conditionally: ```bash @test "A test which should run" { if [ foo != bar ]; then skip "foo isn't bar" fi run foo [ "$status" -eq 0 ] } ``` __Note:__ `setup` and `teardown` hooks still run for skipped tests. ### `setup` and `teardown`: Pre- and post-test hooks You can define special `setup` and `teardown` functions, which run before and after each test case, respectively. Use these to load fixtures, set up your environment, and clean up when you're done. You can also define `setup_file` and `teardown_file`, which will run once before the first test's `setup` and after the last test's `teardown` for the containing file. Variables that are exported in `setup_file` will be visible to all following functions (`setup`, the test itself, `teardown`, `teardown_file`).
Example of setup/setup_file/teardown/teardown_file call order For example the following call order would result from two files (file 1 with tests 1 and 2, and file 2 with test3) beeing tested: ```text setup_file # from file 1, on entering file 1 setup test1 teardown setup test2 teardown teardown_file # from file 1, on leaving file 1 setup_file # from file 2, on enter file 2 setup test3 teardown teardown_file # from file 2, on leaving file 2 ```
### Code outside of test cases You can include code in your test file outside of `@test` functions. For example, this may be useful if you want to check for dependencies and fail immediately if they're not present. However, any output that you print in code outside of `@test`, `setup` or `teardown` functions must be redirected to `stderr` (`>&2`). Otherwise, the output may cause Bats to fail by polluting the TAP stream on `stdout`. ### File descriptor 3 (read this if Bats hangs) Bats makes a separation between output from the code under test and output that forms the TAP stream (which is produced by Bats internals). This is done in order to produce TAP-compliant output. In the [Printing to the terminal](#printing-to-the-terminal) section, there are details on how to use file descriptor 3 to print custom text properly. A side effect of using file descriptor 3 is that, under some circumstances, it can cause Bats to block and execution to seem dead without reason. This can happen if a child process is spawned in the background from a test. In this case, the child process will inherit file descriptor 3. Bats, as the parent process, will wait for the file descriptor to be closed by the child process before continuing execution. If the child process takes a lot of time to complete (eg if the child process is a `sleep 100` command or a background service that will run indefinitely), Bats will be similarly blocked for the same amount of time. **To prevent this from happening, close FD 3 explicitly when running any command that may launch long-running child processes**, e.g. `command_name 3>&-` . ### Printing to the terminal Bats produces output compliant with [version 12 of the TAP protocol][TAP]. The produced TAP stream is by default piped to a pretty formatter for human consumption, but if Bats is called with the `-t` flag, then the TAP stream is directly printed to the console. This has implications if you try to print custom text to the terminal. As mentioned in [File descriptor 3](#file-descriptor-3-read-this-if-bats-hangs), bats provides a special file descriptor, `&3`, that you should use to print your custom text. Here are some detailed guidelines to refer to: - Printing **from within a test function**: - To have text printed from within a test function you need to redirect the output to file descriptor 3, eg `echo 'text' >&3`. This output will become part of the TAP stream. You are encouraged to prepend text printed this way with a hash (eg `echo '# text' >&3`) in order to produce 100% TAP compliant output. Otherwise, depending on the 3rd-party tools you use to analyze the TAP stream, you can encounter unexpected behavior or errors. - The pretty formatter that Bats uses by default to process the TAP stream will filter out and not print text output to file descriptor 3. - Text that is output directly to stdout or stderr (file descriptor 1 or 2), ie `echo 'text'` is considered part of the test function output and is printed only on test failures for diagnostic purposes, regardless of the formatter used (TAP or pretty). - Printing **from within the `setup` or `teardown` functions**: The same hold true as for printing with test functions. - Printing **outside test or `setup`/`teardown` functions**: - Regardless of where text is redirected to (stdout, stderr or file descriptor 3) text is immediately visible in the terminal. - Text printed in such a way, will disable pretty formatting. Also, it will make output non-compliant with the TAP spec. The reason for this is that each test file is evaluated n+1 times (as mentioned [earlier](#writing-tests)). The first run will cause such output to be produced before the [_plan line_][tap-plan] is printed, contrary to the spec that requires the _plan line_ to be either the first or the last line of the output. - Due to internal pipes/redirects, output to stderr is always printed first. [tap-plan]: https://testanything.org/tap-specification.html#the-plan ### Special variables There are several global variables you can use to introspect on Bats tests: - `$BATS_TEST_FILENAME` is the fully expanded path to the Bats test file. - `$BATS_TEST_DIRNAME` is the directory in which the Bats test file is located. - `$BATS_TEST_NAMES` is an array of function names for each test case. - `$BATS_TEST_NAME` is the name of the function containing the current test case. - `$BATS_TEST_DESCRIPTION` is the description of the current test case. - `$BATS_TEST_NUMBER` is the (1-based) index of the current test case in the test file. - `$BATS_SUITE_TEST_NUMBER` is the (1-based) index of the current test case in the test suite (over all files). - `$BATS_TMPDIR` is the location to a directory that may be used to store temporary files. - `$BATS_FILE_EXTENSION` (default: `bats`) specifies the extension of test files that should be found when running a suite (via `bats [-r] suite_folder/`) ### Libraries and Add-ons Bats supports loading external assertion libraries and helpers. Those under `bats-core` are officially supported libraries (integration tests welcome!): - - common assertions for Bats - - supporting library for Bats test helpers - - common filesystem assertions for Bats - - e2e tests of applications in K8s environments and some external libraries, supported on a "best-effort" basis: - (still relevant? Requires review) - (as per #147) - (how is this different from grayhemp/bats-mock?)