Testing

test blocks and the assert family: a program checks its own results and prints which tests passed and which failed. Run a cell to see its output beside the expected one.

A passing test

assert_near(a, b, tol) inside a named test block. What prints is the name — one line per test, however many assertions are inside.

Viv [1]

test "pythagoras" {
    assert_near(sqrt(3.0 * 3.0 + 4.0 * 4.0), 5.0, 1.0e-12)
}

A failing test says what failed

The FAIL line names the test and shows the failing assertion's values, so you see which check failed and by how much.

Viv [2]

test "wrong on purpose" {
    assert_near(2.0 + 2.0, 5.0, 1.0e-9)
}

Test a function against a property

Check a function against a mathematical fact it must satisfy (here, the partial sums of 1/k! converge to e), not only against fixed values.

Viv [3]

def esum(n) {
    s = 0.0
    for i to n {
        s += 1.0 / gamma(i + 1.0)
    }
    return s
}
test "partial sums of 1/k! approach e" {
    assert_near(esum(20.0), exp(1.0), 1.0e-12)
}

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