@test
operation integers() {
  assertEquals(2, 1 + 1);
  assertNotEquals(10, 1 + 1);
}

@test
operation floats() {
  // Floating-point math: 0.01 * 10 is not exactly equal to 0.1
  assertNotEquals(0.1, 0.01 * 10);

  // We need to define an error margin. We use ulps, as in Math.ulp(double).
  // Here we use a margin of 10 ulps around the expected value (0.1). 
  assertEquals(0.1, 0.01 * 10, 10);
}

@test
operation strings() {
  // assertEquals also works with Strings
  assertEquals("A", "A");
  assertNotEquals("A", "B");
}

@test
operation errors() {
  // assertError only passes if an exception is thrown when evaluating its expression
  assertError(null.toString());
}

@test
operation customAssertion() {
  assertStringContainsFoo("FooBar");
  assertError(assertStringContainsFoo("Bar"));
}

operation assertStringContainsFoo(s: String) {
  if (not s.contains("Foo")) {
    fail("String '" + s + "' did not contain Foo");
  }
}