68 lines
2 KiB
Markdown
68 lines
2 KiB
Markdown
# Testing
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The Rust language has a facility for testing built into the language.
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Tests can be interspersed with other code, and annotated with the
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`#[test]` attribute.
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use std;
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fn twice(x: int) -> int { x + x }
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#[test]
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fn test_twice() {
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let i = -100;
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while i < 100 {
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assert twice(i) == 2 * i;
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i += 1;
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}
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}
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When you compile the program normally, the `test_twice` function will
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not be used. To actually run the tests, compile with the `--test`
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flag:
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> rustc --lib twice.rs
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> ./twice
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running 1 tests
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test test_twice ... ok
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result: ok. 1 passed; 0 failed; 0 ignored
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Or, if we change the file to fail, for example by replacing `x + x`
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with `x + 1`:
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running 1 tests
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test test_twice ... FAILED
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failures:
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test_twice
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result: FAILED. 0 passed; 1 failed; 0 ignored
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You can pass a command-line argument to a program compiled with
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`--test` to run only the tests whose name matches the given string. If
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we had, for example, test functions `test_twice`, `test_once_1`, and
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`test_once_2`, running our program with `./twice test_once` would run
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the latter two, and running it with `./twice test_once_2` would run
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only the last.
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To indicate that a test is supposed to fail instead of pass, you can
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give it a `#[should_fail]` attribute.
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use std;
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fn divide(a: float, b: float) -> float {
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if b == 0f { fail; }
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a / b
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}
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#[test]
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#[should_fail]
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fn divide_by_zero() { divide(1f, 0f); }
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To disable a test completely, add an `#[ignore]` attribute. Running a
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test runner (the program compiled with `--test`) with an `--ignored`
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command-line flag will cause it to also run the tests labelled as
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ignored.
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A program compiled as a test runner will have the configuration flag
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`test` defined, so that you can add code that won't be included in a
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normal compile with the `#[cfg(test)]` attribute (see [conditional
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compilation](syntax.md#conditional)).
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