Cargo test suite reported one or more test failures

What this failure means

One or more Rust tests failed. The cargo test runner reported individual failures with test X ... FAILED and the suite summary shows failures: N tests failed.

Symptoms

Faultline looks for one or more of these log fragments:

test result: FAILED
test.*\.\.\.\s*FAILED
failures:
FAILED tests
error\[E

Diagnosis

cargo test terminated with a non-zero exit code. Individual failing tests are reported as:

test path::to::test_name ... FAILED

failures:

---- path::to::test_name stdout ----
thread 'main' panicked at 'assertion `left == right` failed', src/lib.rs:42

failures:
    path::to::test_name

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out

Common causes:

• Assertion failure — assert_eq!, assert!, or panic! did not hold; the implementation changed or a test expectation is stale.
• Panic in test — the code under test panicked (index out of bounds, unwrap on None, etc.).
• Compile error in test — the test file has a type error or missing dependency; cargo test reports error[E...] before the test run.
• Thread panic — a spawned thread panicked and the test did not catch it.

Fix steps

1. Reproduce locally:

   cargo test
   cargo test -- --nocapture  # show stdout from failing tests
   

2. Run only the failing test:

   cargo test path::to::test_name
   cargo test test_name -- --nocapture
   

3. Read the panic message and backtrace:

   RUST_BACKTRACE=1 cargo test path::to::test_name -- --nocapture
   

4. For assert_eq! failures, the output shows both left and right values — identify which side changed.

5. For compile errors in tests, run cargo check --tests to see all type errors without executing tests.

Validation

• cargo test exits zero.
• Individual test: cargo test path::to::test_name passes.

Why it matters

Cargo test failures are deterministic and block the pipeline. The failure output names the exact test function and the assertion that failed, making root-cause analysis straightforward. Even a single test failure returns a non-zero exit code, preventing downstream publish or deploy steps.

Prevention

• Run cargo test as a pre-push hook.
• Use cargo test -- --nocapture locally to see all output during development.
• Keep tests hermetic: avoid relying on file paths, environment variables, or network access in unit tests.

Try it locally

cargo test
cargo test -- --nocapture
RUST_BACKTRACE=1 cargo test -- --nocapture
cargo test

How Faultline detects it

Use faultline explain cargo-test-failure to see the full playbook.

faultline analyze build.log
faultline explain cargo-test-failure

Generated from playbooks/bundled/log/test/cargo-test-failure.yaml. Do not edit directly.