Assert_eq
The Rust assert_eq! macro compares two expressions and panics when their evaluated values are unequal, reporting the compared values.
Learn Rust in a Month of Lunches
assert_eq! is a Rust macro that panics when two expressions evaluate to unequal values and reports both values.
- How it is used
- Uses equality assertions to encode guarantees in ordinary code, documentation examples, and automated tests.
- How deep it goes
- Explains comparison, panic behavior, custom messages, collection checks, and test diagnostics without detailing macro expansion internals.
- Examples
- Demonstrates even-number validation, Vec mutations, custom messages, and failed tests comparing 2 with 3.
- What you can do after
- Apply it to verify equal values and diagnose mismatches in Rust programs and tests.
Read how Learn Rust in a Month of Lunches explains assert_eq →
Refactoring to Rust
The Rust assert_eq! macro compares two values for equality and panics when they differ.
- How it is used
- Uses equality assertions to validate expected results in Rust tests and other Rust code.
- How deep it goes
- Explains comparison, panic behavior, captured failures, and Debug output, but does not cover macro internals.
- Examples
- Demonstrates 2 + 2 equaling 4, deliberately failing against 5, and inspecting output from passing and failing tests.
- What you can do after
- Apply it via Rust’s test framework to compare values and diagnose failures from reported left and right values.
Related concepts
- testuses · A test is a procedure or check that evaluates behavior using specified inputs or evidence against expected results or criteria.
- documentationused by · Documentation is recorded explanatory, instructional, or reference information that describes a subject, system, or process to support its understanding, use, or maintenance.
- paniccontrasts with · A panic is a runtime failure mechanism that abruptly stops ordinary execution when an unrecoverable error or violated assumption prevents safe continuation.
- arrayuses · An array is an indexed, ordered collection of elements arranged in one or more dimensions, with elements accessed by position.
- println! macroalternative to · The println! macro is an output operation that formats arguments and writes the resulting text followed by a line terminator to standard output.
- assertionalternative to · A software assertion is an executable check of an expected condition or property that signals failure when the check does not hold.
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