Matchers with expect()

The entry point of any assertion is expect(value). From there you chain a matcher that describes what the value must satisfy. If the condition fails, the runner reports the test as failed with a clear message.

The most common matchers cover equality, collection size, membership, and string comparison:

Runs via zolo test. Demonstrates to_eq, to_start_with, to_have_len, to_contain, to_be_empty, and the .not inversion.

01-expect.zolo

Playground

// Demonstrates the expect() matcher library (T4).

@test
fn matchers_basicos() {
  expect(2 + 2).to_eq(4)
  expect("data:image/png;base64,AAA").to_start_with("data:image/png;base64,")
  expect([10, 20]).to_have_len(2)
  expect([10, 20]).to_contain(20)
  expect("").to_be_empty()
  expect(1).not.to_eq(2)
}

Requires the Zolo CLI/host — open in the playground or run locally.

The .not chain inverts any matcher — expect(1).not.to_eq(2) asserts that two values are different.

Challenge

Add an expect("zolo").to_end_with("lo") to the example and run zolo test. Then try .not.to_end_with("lo") and observe the failure message.