Hi,
Rust presently has no "standard" mechanism for unit testing. I'd like to
adopt one, or at least move towards having one. We're getting enough
library written-in-rust code now that it makes sense.
I'm interested in pursuing a slightly-structured technique, and have
been considering a mechanism similar to the D 'version' and 'unittest'
system(s).
The idea has three parts:
1. Add a command-line flag to specify a set of configuration flags to
enable during a particular build. say -cfg win32 or such. These are not
structured values, just opaque strings.
2. Add a syntax extension also called cfg that marks an item as
to-be-included only if one of its arguments appears in the set of
configuration flags.
With 1 and 2, we'd be at the point where a module marked as, say,
"#cfg(test) mod test { ... }" would wind up conditionally compiled only
if you ran the compiler with -cfg test. (This would also double as a
mechanism for including modules on a per-platform basis, including debug
code, that sort of thing.) But programmers are lazy. So let's go one
step further:
3. Add a *further* command-line flag called '-test' that does two things:
- Adds #cfg(test) to the set of config flags, so all test-conditional
code gets included.
- Changes the target the compiler's building. Instead of groveling
for a main function, or just building a library (as in -shared),
the -test target is a synthetic target that runs every function
marked with #test, passing in a value of type std.test.harness,
a basic xUnit-ish test harness.
(should also provide runtime subset-selection of tests in the
harness, etc, etc., but you get the idea)
If this works out nicely, we can expand the interface a bit in the
future to include specifying a test harness rather than hard-wiring it
to the one in std. For the time being I'd be happy to have any sort of
structured system, and I'd prefer to err on the side of "discoverable"
rather than "configurable" for testing.
(Also, this way we increase the odds of the standard-library one
maturing along with community needs, rather than rotting away. Nothing
sadder than a standard library component nobody uses!)
Comments? Preferences?
-Graydon
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