面向 C++ 程序员的测试模式
你将学到： Rust 内置测试框架——
#[test]、#[should_panic]、返回Result的测试、测试数据的构建器模式、基于 Trait 的 mock、proptest属性测试、insta快照测试，以及集成测试组织。零配置测试，替代 Google Test + CMake。
C++ 测试通常依赖外部框架（Google Test、Catch2、Boost.Test）与复杂构建集成。Rust 测试框架内置于语言与工具链——无依赖、无 CMake 集成、无测试运行器配置。
#[test] 之外的测试属性
#![allow(unused)]
fn main() {
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn basic_pass() {
assert_eq!(2 + 2, 4);
}
// Expect a panic — equivalent to GTest's EXPECT_DEATH
#[test]
#[should_panic]
fn out_of_bounds_panics() {
let v = vec![1, 2, 3];
let _ = v[10]; // Panics — test passes
}
// Expect a panic with a specific message substring
#[test]
#[should_panic(expected = "index out of bounds")]
fn specific_panic_message() {
let v = vec![1, 2, 3];
let _ = v[10];
}
// Tests that return Result<(), E> — use ? instead of unwrap()
#[test]
fn test_with_result() -> Result<(), String> {
let value: u32 = "42".parse().map_err(|e| format!("{e}"))?;
assert_eq!(value, 42);
Ok(())
}
// Ignore slow tests by default — run with `cargo test -- --ignored`
#[test]
#[ignore]
fn slow_integration_test() {
std::thread::sleep(std::time::Duration::from_secs(10));
}
}
}cargo test # Run all non-ignored tests
cargo test -- --ignored # Run only ignored tests
cargo test -- --include-ignored # Run ALL tests including ignored
cargo test test_name # Run tests matching a name pattern
cargo test -- --nocapture # Show println! output during tests
cargo test -- --test-threads=1 # Run tests serially (for shared state)
测试辅助：测试数据的构建器模式
C++ 中用 Google Test fixture（class MyTest : public ::testing::Test）。
Rust 中用构建函数或 Default Trait：
#![allow(unused)]
fn main() {
#[cfg(test)]
mod tests {
use super::*;
// Builder function — creates test data with sensible defaults
fn make_gpu_event(severity: Severity, fault_code: u32) -> DiagEvent {
DiagEvent {
source: "accel_diag".to_string(),
severity,
message: format!("Test event FC:{fault_code}"),
fault_code,
}
}
// Reusable test fixture — a set of pre-built events
fn sample_events() -> Vec<DiagEvent> {
vec![
make_gpu_event(Severity::Critical, 67956),
make_gpu_event(Severity::Warning, 32709),
make_gpu_event(Severity::Info, 10001),
]
}
#[test]
fn filter_critical_events() {
let events = sample_events();
let critical: Vec<_> = events.iter()
.filter(|e| e.severity == Severity::Critical)
.collect();
assert_eq!(critical.len(), 1);
assert_eq!(critical[0].fault_code, 67956);
}
}
}用 Trait 做 mock
C++ 中 mock 需 Google Mock 或手动虚函数覆盖。 Rust 中为依赖定义 Trait，在测试中替换实现：
#![allow(unused)]
fn main() {
// Production trait
trait SensorReader {
fn read_temperature(&self, sensor_id: u32) -> Result<f64, String>;
}
// Production implementation
struct HwSensorReader;
impl SensorReader for HwSensorReader {
fn read_temperature(&self, sensor_id: u32) -> Result<f64, String> {
// Real hardware call...
Ok(72.5)
}
}
// Test mock — returns predictable values
#[cfg(test)]
struct MockSensorReader {
temperatures: std::collections::HashMap<u32, f64>,
}
#[cfg(test)]
impl SensorReader for MockSensorReader {
fn read_temperature(&self, sensor_id: u32) -> Result<f64, String> {
self.temperatures.get(&sensor_id)
.copied()
.ok_or_else(|| format!("Unknown sensor {sensor_id}"))
}
}
// Function under test — generic over the reader
fn check_overtemp(reader: &impl SensorReader, ids: &[u32], threshold: f64) -> Vec<u32> {
ids.iter()
.filter(|&&id| reader.read_temperature(id).unwrap_or(0.0) > threshold)
.copied()
.collect()
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn detect_overtemp_sensors() {
let mut mock = MockSensorReader { temperatures: Default::default() };
mock.temperatures.insert(0, 72.5);
mock.temperatures.insert(1, 91.0); // Over threshold
mock.temperatures.insert(2, 65.0);
let hot = check_overtemp(&mock, &[0, 1, 2], 80.0);
assert_eq!(hot, vec![1]);
}
}
}测试中的临时文件与目录
C++ 测试常用平台相关临时目录。Rust 有 tempfile：
#![allow(unused)]
fn main() {
// Cargo.toml: [dev-dependencies]
// tempfile = "3"
#[cfg(test)]
mod tests {
use super::*;
use tempfile::NamedTempFile;
use std::io::Write;
#[test]
fn parse_config_from_file() -> Result<(), Box<dyn std::error::Error>> {
// Create a temp file that's auto-deleted when dropped
let mut file = NamedTempFile::new()?;
writeln!(file, r#"{{"sku": "ServerNode", "level": "Quick"}}"#)?;
let config = load_config(file.path().to_str().unwrap())?;
assert_eq!(config.sku, "ServerNode");
Ok(())
// file is deleted here — no cleanup code needed
}
}
}用 proptest 做基于属性的测试
不写具体用例，而描述对所有输入都应成立的不变式。
proptest 生成随机输入并找最小失败用例：
#![allow(unused)]
fn main() {
// Cargo.toml: [dev-dependencies]
// proptest = "1"
#[cfg(test)]
mod tests {
use proptest::prelude::*;
fn parse_and_format(n: u32) -> String {
format!("{n}")
}
proptest! {
#[test]
fn roundtrip_u32(n: u32) {
let formatted = parse_and_format(n);
let parsed: u32 = formatted.parse().unwrap();
prop_assert_eq!(n, parsed);
}
#[test]
fn string_contains_no_null(s in "[a-zA-Z0-9 ]{0,100}") {
prop_assert!(!s.contains('\0'));
}
}
}
}用 insta 做快照测试
对产生复杂输出（JSON、格式化字符串）的测试，insta 自动生成并管理参考快照：
#![allow(unused)]
fn main() {
// Cargo.toml: [dev-dependencies]
// insta = { version = "1", features = ["json"] }
#[cfg(test)]
mod tests {
use insta::assert_json_snapshot;
#[test]
fn der_entry_format() {
let entry = DerEntry {
fault_code: 67956,
component: "GPU".to_string(),
message: "ECC error detected".to_string(),
};
// First run: creates a snapshot file in tests/snapshots/
// Subsequent runs: compares against the saved snapshot
assert_json_snapshot!(entry);
}
}
}cargo insta test # Run tests and review new/changed snapshots
cargo insta review # Interactive review of snapshot changes
C++ vs Rust 测试对照
| C++（Google Test） | Rust | 说明 |
|---|---|---|
TEST(Suite, Name) { } | #[test] fn name() { } | 无需 suite/类层次 |
ASSERT_EQ(a, b) | assert_eq!(a, b) | 内置宏，无需框架 |
ASSERT_NEAR(a, b, eps) | assert!((a - b).abs() < eps) | 或使用 approx crate |
EXPECT_THROW(expr, type) | #[should_panic(expected = "...")] | 或 catch_unwind 精细控制 |
EXPECT_DEATH(expr, "msg") | #[should_panic(expected = "msg")] | |
class Fixture : public ::testing::Test | 构建函数 + Default | 无需继承 |
Google Mock MOCK_METHOD | Trait + 测试 impl | 更显式，无宏魔法 |
INSTANTIATE_TEST_SUITE_P（参数化） | proptest! 或宏生成测试 | |
SetUp() / TearDown() | 通过 Drop 的 RAII——清理自动 | 测试结束变量 drop |
| 独立测试二进制 + CMake | cargo test——零配置 | |
ctest --output-on-failure | cargo test -- --nocapture |
集成测试：tests/ 目录
单元测试在 #[cfg(test)] module 中与代码同处。集成测试位于 crate 根目录独立 tests/，像外部使用者一样测试库公开 API：
my_crate/
├── src/
│ └── lib.rs # Your library code
├── tests/
│ ├── smoke.rs # Each .rs file is a separate test binary
│ ├── regression.rs
│ └── common/
│ └── mod.rs # Shared test helpers (NOT a test itself)
└── Cargo.toml
#![allow(unused)]
fn main() {
// tests/smoke.rs — tests your crate as an external user would
use my_crate::DiagEngine; // Only public API is accessible
#[test]
fn engine_starts_successfully() {
let engine = DiagEngine::new("test_config.json");
assert!(engine.is_ok());
}
#[test]
fn engine_rejects_invalid_config() {
let engine = DiagEngine::new("nonexistent.json");
assert!(engine.is_err());
}
}#![allow(unused)]
fn main() {
// tests/common/mod.rs — shared helpers, NOT compiled as a test binary
pub fn setup_test_environment() -> tempfile::TempDir {
let dir = tempfile::tempdir().unwrap();
std::fs::write(dir.path().join("config.json"), r#"{"log_level": "debug"}"#).unwrap();
dir
}
}#![allow(unused)]
fn main() {
// tests/regression.rs — can use shared helpers
mod common;
#[test]
fn regression_issue_42() {
let env = common::setup_test_environment();
let engine = my_crate::DiagEngine::new(
env.path().join("config.json").to_str().unwrap()
);
assert!(engine.is_ok());
}
}运行集成测试：
cargo test # Runs unit AND integration tests
cargo test --test smoke # Run only tests/smoke.rs
cargo test --test regression # Run only tests/regression.rs
cargo test --lib # Run ONLY unit tests (skip integration)
与单元测试的关键区别：集成测试不能访问私有函数或
pub(crate)项。这迫使你验证公开 API 是否足够——是有价值的设计信号。C++ 术语下，类似只测公开头文件、无friend访问。