test and expect

Learn assertions with test and expect.

test and expect

test('name', () { ... }) opens a test block. Inside it you make claims with expect(actual, matcher). For example expect(square(4), equals(16)) probes the square function.

Matchers include equals(x), isTrue, isFalse and throwsException. Each checks a different condition.

A test can hold several expect calls. If the first fails the test stops and the rest do not run.

Matchers

Matchers check different conditions. equals(x) tests equality, isTrue truth, isFalse falsity, throwsException error throwing.

For example expect(parse('x'), throwsFormatException) expects an error. If the error is thrown the test is green; otherwise red.

Matchers make a test readable. expect(x, isNotNull) reads more clearly than expect(x == null, isFalse).

Exercise The square function

Write a function int square(int n) => n * n;. In main print the result of square(4) with print.

Show example solution

int square(int n) => n * n;

void main() {
  print(square(4));
}

Test yourself

What does expect(actual, expected) do?
- Compares actual and expected values
- Opens a file
- Sets up a loop
- Throws an error
Show answer

Compares actual and expected values — expect compares the actual and expected values.

The expect call

expect(square(4), ____(16));

Show answer

expect(square(4), equals(16));

What does throwsException probe?
- Value equality
- That an error is thrown
- End of a loop
- Existence of a file
Show answer

That an error is thrown — throwsException probes that an error is thrown.

Next lesson: group

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