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Tests sit next to the code they check, with nothing to install

A file keeps its tests in a tests: block. Each it("name"): is one test case, and it may call the file's private functions, so you test the real helper, not a copy made public for the test. it_each runs one case per row of a table. The assertions come from std.testing, and hd test runs the cases, so there is no test framework to pick or configure. Test code is compiled only for testing, so none of it ships in the program.

Test: Ctrl+Enter · Pages: Alt+← Alt+→

fn shipping_cents(weight_grams: i32) -> i32:  # ← private, and still testable    if weight_grams <= 1000: 499 else: 499 + (weight_grams - 1000) / 500 * 150tests:    use std.testing.it_each    it("a parcel up to 1 kg pays the base rate"):        assert_equal(shipping_cents(800), 499, reason="base rate")    it_each("each full 500 g over 1 kg adds 150", [(1500, 649), (2400, 799)], body=fn!(row: (i32, i32)):        let (grams, cents) = row        assert_equal(shipping_cents(grams), cents, reason="per 500 g")    )# Press Test. Then change the first 499, the base rate, to 450# and press Test again:#     assertion-failed: base rate: actual 450, expected 499# ── plumbing ──

Press Test to run the tests.