Advent of PBT 2021 — Learn how to use property based testing and fast-check through examples
Our algorithm today is: detectCycleInLinkedList.
It comes with the following documentation and prototype:
/**
* Definition of a LinkedList
*/
export type LinkedList = {
value: number;
next: LinkedList | undefined;
};
/**
* Check if there is a cycle in a given linked list.
*
* @param list - The linked list to check.
*
* @returns
* true if there is a cycle, false otherwise.
*/
declare function detectCycleInLinkedList(list: LinkedList): boolean;
We already wrote some examples based tests for it:
it("should not detect any cycle for a one-element list", () => {
const list: LinkedList = {
value: 0,
next: undefined
};
expect(detectCycleInLinkedList(list)).toBe(false);
});
it("should not detect any cycle for a two-element list", () => {
const list: LinkedList = {
value: 0,
next: { value: 1, next: undefined }
};
expect(detectCycleInLinkedList(list)).toBe(false);
});
it("should not detect any cycle for a list with duplicates", () => {
const list: LinkedList = {
value: 0,
next: { value: 0, next: undefined }
};
expect(detectCycleInLinkedList(list)).toBe(false);
});
it("should detect a cycle if a node appear twice", () => {
const list: LinkedList = {
value: 0,
next: undefined
};
list.next = list;
expect(detectCycleInLinkedList(list)).toBe(true);
});
How would you cover it with Property Based Tests?
In order to ease your task we provide you with an already setup CodeSandbox, with examples based tests already written and a possible implementation of the algorithm: https://codesandbox.io/s/advent-of-pbt-day-4-g0jdy?file=/src/index.spec.ts&previewwindow=tests
You wanna see the solution? Here is the set of properties I came with to cover today's algorithm: https://dev.to/dubzzz/advent-of-pbt-2021-day-4-solution-lh2
Back to "Advent of PBT 2021" to see topics covered during the other days and their solutions.
More about this serie on @ndubien or with the hashtag #AdventOfPBT.
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