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docs: Change recommendation for include_str! in tests

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They should use relative paths for the files. This is documented as the
expected use in https://doc.rust-lang.org/std/macro.include_str.html and
allows us to avoid using CARGO_MANIFEST_DIR in the tests.

BUG=b:370352548
TEST=tools/presubmit

Change-Id: I97ca771c54275859c0c4a293084de68af78ce914
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/6159966
Commit-Queue: Devin Moore <devinmoore@google.com>
Reviewed-by: Daniel Verkamp <dverkamp@chromium.org>
Reviewed-by: Frederick Mayle <fmayle@google.com>
This commit is contained in:
Devin Moore 2025-01-08 21:20:44 +00:00 committed by crosvm LUCI
parent cabb48dc4d
commit 8fabc8a488
1 changed files with 7 additions and 18 deletions
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25
docs/book/src/testing/index.md
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@ -24,20 +24,12 @@ wine64.
#### File Access in Unit Tests
Some unit tests may need to access extra data files. Instead of relying on relative paths, which can
be fragile and break when tests are executed from different $PWD than the root of the tests' crate,
always utilize the `CARGO_MANIFEST_DIR` environment variable. Cargo sets this variable to the
absolute path of the directory containing manifest of your package.
The `CARGO_MANIFEST_DIR` should be accessed at build time using `env!()` macro, rather than at run
time with functions like `std::env::var()`. This approach is crucial because certain test
environment may require to run the test binaries directly instead of using `cargo test`.
Additionally, it ensures the test binary can be run manually within a debugger like GDB.
To enhance test portability, embed extra data files directly into your Rust binary using the
`include_str!` macro. At runtime, write this data to a temporary file instead of accessing it via
CARGO_MANIFEST_DIR. This avoids hardcoding paths in the binary, ensuring tests function correctly
regardless of the binary or source tree location.
Some unit tests may need to access extra data files. The files should be accessed at build time
using `include_str!()` macro, rather than at run time. The file is located relative to the current
file (similarly to how modules are found). The contents of the file can be used directly in the test
or at runtime the test can write this data to a temporary file. This approach is crucial because
certain test environment may require to run the test binaries directly without access to the source
code. Additionally, it ensures the test binary can be run manually within a debugger like GDB.
These approaches ensure that units tests be able to find the correct paths in various build &
execution environment.
@ -49,10 +41,7 @@ execution environment.
fn test_my_config() {
let temp_file = TempDir::new().unwrap();
let path = temp_file.path().join("my_config.cfg");
let test_config = include_str!(concat!(
env!("CARGO_MANIFEST_DIR"),
"/config/my_config.cfg",
));
let test_config = include_str!("../../../data/config/my_config.cfg");
fs::write(&path, test_config).expect("Unable to write test file");
let config_file = File::open(path).expect("Failed to open config file");
// ... rest of your test ...