--- title: "**echo**(1) acceptance tests" author: Lars Wirzenius / The Fable project ... Introduction ============================================================================= **echo**(1) is a Unix command line tool, which writes its command line arguments to the standard output. This is a simple acceptance test suite for the `/bin/echo` implementation. No arguments ============================================================================= This scenario runs `/bin/echo` without arguments and checks that it outputs a single newline character to the standard output, nothing to the standard error, and exits with a zero exit code. ```fable when user runs echo without arguments then exit code is 0 and standard output contains a newline and standard error is empty ``` Hello, world ============================================================================= This scenario runs `/bin/echo` to produce the output "hello, world". ```fable when user runs echo with arguments hello, world then exit code is 0 and standard output contains "hello, world" and standard error is empty ```