README.md

Test Driven Development By Example

area: test-driven-by-example

• the author: Kent Beck

This project is implemented example codes by TypeScript.

Getting Started

pnpm install
pnpm test

Test Environment

I follow this link 👉 How to run the Node built-in testrunner for TypeScript files inside a specific directory? · Issue #3902 · nodejs/help

This LTS version's Node.js shows the warning: ExperimentalWarning: Custom ESM Loaders is an experimental feature and might change at any time

That must be standard feature in the future.

Node.js has to use loader to run TypeScript.

TypeScript runtime comparisons

Motivation

Use standard Node.js's functions

Notes

This node version is expected over 20 currently. As tsup, node:test is not propper solving in build process.

I hope this:

tsup src/money.test.ts

Conclusion

Test Driven Development By Example has some technical issues that is occurred by legacy programming environment, but the article is still useful book.

Kent Beck shows the way to implement the code from his idea. Some implementation looks winding road, but test case is very clear.

Currently we have more choices for TDD that is type system, integration test and maybe Model Checking.

Circular Reference

In money package, each modules uses Factory method, but it occurs the technical issue about circular reference. In addition, the actual error message is TypeError: Class extends value undefined is not a constructor or null

Solution:

This solution looks good 👉 https://jestjs.io/ja/docs/ecmascript-modules

equals method

As Java, when we compare strings, we use equals() method because String is Object. But as TypeScript, it must be === operator because string type is primitive data type.

HashMap is Object in Java that means Key Object must has equals and hashcode method. Lately that must implement Comarable like this:

https://interprism.hatenablog.com/entry/2014/04/04/125444

package jp.co.interprism;

public class HashCompareEqualKey implements Comparable<HashCompareEqualKey> {

    private int num;

    public HashCompareEqualKey(int num) {
        this.num = num;
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        HashCompareEqualKey key = (HashCompareEqualKey) o;
        if (num != key.num) return false;
        return true;
    }

    @Override
    public int hashCode() {
        return num;
    }

    @Override
    public int compareTo(HashCompareEqualKey o) {
        return Integer.compare(num, o.num);
    }
}

In this project, I used tuple because it is easy as TypeScript.

Member variable

In TypeScript Class, member variable can't use method name.

If you use member variable, you must specify this keyword because of distinguishing memeber variable from normal variable.

Down casting

I can't make sense that arg's type is often Object.

Don't do down casting.

Extends class sets super constractor automatically