Testing attributes
The following attributes are used for specifying functions for performing
tests. Compiling a crate in "test" mode enables building the test functions
along with a test harness for executing the tests. Enabling the test mode also
enables the test
conditional compilation option.
The test
attribute
The test
attribute marks a function to be executed as a test. These
functions are only compiled when in test mode. Test functions must be free,
monomorphic functions that take no arguments, and the return type must be one
of the following:
()
Result<(), E> where E: Error
Note: The implementation of which return types are allowed is determined by the unstable
Termination
trait.
Note: The test mode is enabled by passing the
--test
argument torustc
or usingcargo test
.
Tests that return ()
pass as long as they terminate and do not panic. Tests
that return a Result<(), E>
pass as long as they return Ok(())
. Tests that
do not terminate neither pass nor fail.
# #![allow(unused_variables)] #fn main() { # use std::io; # fn setup_the_thing() -> io::Result<i32> { Ok(1) } # fn do_the_thing(s: &i32) -> io::Result<()> { Ok(()) } #[test] fn test_the_thing() -> io::Result<()> { let state = setup_the_thing()?; // expected to succeed do_the_thing(&state)?; // expected to succeed Ok(()) } #}
The ignore
attribute
A function annotated with the test
attribute can also be annotated with the
ignore
attribute. The ignore
attribute tells the test harness to not
execute that function as a test. It will still be compiled when in test mode.
The ignore
attribute may optionally be written with the MetaNameValueStr
syntax to specify a reason why the test is ignored.
# #![allow(unused_variables)] #fn main() { #[test] #[ignore = "not yet implemented"] fn mytest() { // … } #}
Note: The
rustc
test harness supports the--include-ignored
flag to force ignored tests to be run.
The should_panic
attribute
A function annotated with the test
attribute that returns ()
can also be
annotated with the should_panic
attribute. The should_panic
attribute
makes the test only pass if it actually panics.
The should_panic
attribute may optionally take an input string that must
appear within the panic message. If the string is not found in the message,
then the test will fail. The string may be passed using the
MetaNameValueStr syntax or the MetaListNameValueStr syntax with an
expected
field.
# #![allow(unused_variables)] #fn main() { #[test] #[should_panic(expected = "values don't match")] fn mytest() { assert_eq!(1, 2, "values don't match"); } #}