`bats`

a.bats:

strict() { set -euo pipefail; shopt -s inherit_errexit; "$@"; }

setup() {
    [ "$BATS_LIB_PATH" = /usr/lib/bats ] && BATS_LIB_PATH=$HOME/.bats/lib:$BATS_LIB_PATH
    bats_load_library bats-support
    bats_load_library bats-assert
    strict
}

f() { :; }

@test whatever {
    run strict f

    assert_output ''
}

$ docker run --rm -itv "$PWD":/app -w /app alpine:3.21
/ # apk add git bash ncurses
/ # git clone https://github.com/bats-core/bats-core ~/.bats
/ # git clone https://github.com/bats-core/bats-support ~/.bats/lib/bats-support
/ # git clone https://github.com/bats-core/bats-assert ~/.bats/lib/bats-assert
/ # ~/.bats/bin/bats a.bats

ncurses is needed for the pretty formatter.

b.bats:

strict() { set -euo pipefail; shopt -s inherit_errexit; "$@"; }

setup() {
    [ "$BATS_LIB_PATH" = /usr/lib/bats ] && BATS_LIB_PATH=$HOME/.bats/lib:$BATS_LIB_PATH
    bats_load_library bats-support
    bats_load_library bats-assert
    bats_load_library bats-mock/stub.bash
    strict
}

@test whatever {
    stub whatever \
        'a b c : echo output'
    run whatever a b c
    assert_output output
}

teardown() {
    unstub whatever
}

/ # git clone https://github.com/jasonkarns/bats-mock ~/.bats/lib/bats-mock

It only matches the arguments that are in the plan. E.g. if a plan argument is a : :, then the first argument passed to the stub must be a, the rest (if any) are ignored.
The stub must be called at least the specified number of times in the specified order (for the test to pass). E.g. with plan arguments a : :, a b : :, the stub must be called with a, then with a, b.
If there's no : word in a plan argument, the plan argument is considered to have only a command (matches with any arguments). But : makes it match any arguments and invoke :, : makes it match any arguments and invoke an empty command.
If the invocation doesn't match the current plan argument or if it runs out of the plan arguments, the stub exits with 127.
All stubs must be unstubbed in teardown(). Because if a test fails, unstub wouldn't get invoked and the next test will run with stubs from the previous one.
unstub exits with an error if the stub doesn't exist. If unstub is the last argument in teardown() this makes the test fail.

c.bats:

strict() { set -euo pipefail; shopt -s inherit_errexit; "$@"; }

setup() {
    [ "$BATS_LIB_PATH" = /usr/lib/bats ] && BATS_LIB_PATH=$HOME/.bats/lib:$BATS_LIB_PATH
    bats_load_library bats-support
    bats_load_library bats-assert
    bats_load_library bats-mock
    strict
}

@test whatever {
    mock="`mock_create`"
    mock_set_output "$mock" output

    run "$mock" a b c

    [ "`mock_get_call_num "$mock"`" = 1 ]
    [ "`mock_get_call_args "$mock"`" = 'a b c' ]
    assert_output output
}

/ # git clone https://github.com/grayhemp/bats-mock ~/.bats/lib/bats-mock

x-yuri/bats.md

bats

`bats`