[](https://crates.io/crates/subcase)
# Share parts of your test case intuitively
## What is a subcase?
*Sections*, or *subcases* are a cool feature of unit testing frameworks,
such as (awesome) C++ libraries [Catch2](https://github.com/catchorg/Catch2)
and [doctest](https://github.com/doctest/doctest).
Subcases provide an easy way to share code between tests,
like fixtures do, but without needing to move setup and teardown code
outside of your tests' meat, without hassles of object orientation.
How do they work? Subcases allow you to fork function execution
to into different paths which will have common code in the places
you want them to.
Let's look at an example.
```rust
use subcase::with_subcases;
with_subcases! {
#[test]
fn my_test_case() {
let mut v = vec![1,2,3];
subcase! {{
v.push(9);
assert_eq!(v.last().unwrap().clone(), 9);
}}
subcase! {{
v.clear();
assert!(v.is_empty());
for _i in 0..4 { v.push(1); }
}}
assert_eq!(v.len(), 4);
assert!(v.capacity() >= 4);
}
}
```
`my_test_case`'s body will be executed twice, first time
with first `subcase!{{...}}` block, ignoring the second,
and vice versa.
That's not all! Subcases can be nested! Replace the body
with this code:
```rust
let mut v = vec![1,2,3];
subcase! {{
v.push(9);
}}
subcase! {{
v.clear();
subcase! {{
for _i in 0..5 { v.push(1); }
assert_eq!(v.len(), 5);
}}
v.push(100);
subcase! {{
v.extend_from_slice(&[4,5,6,7,8]);
}}
assert_eq!(v.len(), 6);
v.pop();
v.pop();
}}
assert_eq!(v.len(), 4);
```
Test function body is executed 3 times: once
for each of leaf subcases (i.e. not containing more nested subcases),
while the big parent subcase is entered twice.
You can write only one subcase or no subcases at all, function
will run as usual.
## Other oprions?
Indeed, there are already a few crates that implement the concept
of subcases:
+ [rust-catch](https://github.com/guydunton/rust-catch)
+ [crossroads](https://crates.io/crates/crossroads)
What distinguishes subcase crate from each of them, is that
subcase only uses lightweight declarative (i.e. `macro_rules!`)
macros and has zero dependencies. Also, `with_subcases` macro stuffs
all execution paths inside one function, instead of generating
many. These making it very easy on Rust compiler, in comparison
to the mentioned crates.
(I will provide actual benchmarks in the future.)
## Limitations
One technical consequence of how the crate was
implemented is that subcases from one test function can't run
in parallel. This may or may not slow down your tests' execution.
If you have a lot of fine-grained test cases, you should be fine.
Another thing is that nesting subcases is limited. Currently the hard
upper bound is 16. (I think, it's not practical to have more than two
level of subcases.)
Also, as different branches of evaluation are switched at runtime,
you possibly can trigger borrow checker.
There are also limitations that potentially will be lifted in the
future:
+ Rust built-in testing framework cannot help you
know what exact path of execution has failed.
+ You must use double pair of braces with inner `subcase!` macro.
+ You cannot rename the inner `subcase!` macro.
## License
Licensed under MIT License.