expect:
        assertValueIs([b: '2', c: '3', d: '4'])

        when:
        def execTimeValue = property.calculateExecutionTimeValue()

        then:
        assertEqualValues([b: '2', c: '3', d: '4'], execTimeValue.toValue().get())
    }

    def "execution time value is missing if any undefined-safe operations are performed in the tail"() {
        given:

    protected void assertPropertyValueIs(T expected, PropertyInternal<?> property) {
        assert property.present
        T actual = property.get()
        assertEqualValues(expected, actual)
    }

    protected void assertEqualValues(T expected, T actual) {
        assert actual == expected
    }

    def "cannot get value when it has none"() {
        given:
        def property = propertyWithNoValue()

    }

    def property = property()

    protected void assertValueIs(C expected, PropertyInternal<?> property = this.property) {
        assertPropertyValueIs(expected, property)
    }

    protected void assertEqualValues(C expected, C actual) {
        assert actual instanceof ImmutableCollection
        assert immutableCollectionType.isInstance(actual)
        assertCollectionIs(actual, expected)
    }