Let's start with - the obvious. You need to get your basics straight.
I am looking to test out day trading strategies. Most strategies I am
interested in require to hold onto the stock for a week or more.
You want a vegetarian steak? Because either something is DAY trading, or it is not. And DAY trading is not "holding stock for a week or more". This sentence makes NO sense except assuming you talk of 2 sets of strategies here, in which case it makes still no sense because the second sentence provides zero relevant information, so why do you even raise them? This is important - because day trading has a: limitations in the USA (otherwise you are not allowed to day trade) and b: often uses specialized brokers (which allow a lot of fancy features and have a LOT lower prices than other brokers).
What are common techniques for doing this?
It is called a "Backtest" and it is EXTREMELY common - so common you will have had to be extremely limited in your experience to NOT have used a platform at times or read marketing material from your broker at times trying to sell you access to a backtest platform. This is like saying "I drive cars for 40 years, what the heck is a navigation system, I never heard of them". And yes, this stuff is really that common.
Basically, unless you live in a world with a VERY Limited broker access, you can connect to it with other platforms and there are a LOT of them that (a) facilitate automatic tests (i.e trading strategies) and (b) allow automated testing of said strategies with provided historical data, or (in case of Ninja Trader, i.e.) allow you to play forward old data for manual trading. I particularly like that NInja Trader feature (not that I like Ninja Trader a lot) because for some things it is really nice to "pretend" to have life data. Training, i.e. (training the basics of trading, demonstrating what a stop is etc.) - stuff you can not wait for a market "to behave".
This is SO common that companies make money selling it. Among them:
- Ninja Trader
- MetaTrader, though that is used more in Forex and offered by many brokers
To name just a few. If you ever read any site, or click and advertising - google has likely tried to drawn you in advertisings for them.
Now, there are limits and this is a wide field. A word of warning - this is not as easy as it sounds, it goes a lot into the direction of snake oil FOR MOST PEOPLE. I.e. it is not a magic wand you install and a month later you are rich. You CAN make good money with this, but you first need to learn proper trading and be VERY aware of the possible pitfalls, of which there are many. There are whole books written about them, so no, this is too broad a field for this. Let's just say that if you can not make money without backtesting, you likely can not make money with it either. Like anything day trading related, you leave the "I have a job" area fast and this turns into your job. And sadly for many people making money is totally optional in this job. Which means it never happens.
Oh, and you will need some historical data for testing, obviously.