I have an idea for encryption that I could program fairly easily to encrypt some local text file.
Given that my approach is novel, and does not use any of the industry standard encryption techniques, would I be able to test the strength of my encryption using 'cracker' apps or suchlike?
Or do all those tools rely on advanced knowledge of the encryption process (or intercepted 'keys'), meaning I'd have to build my own cracker for testing?
If you've written your own "novel" encryption, without any "industry standard encryption techniques", and you don't know how to test it (ie: you are not an expert cryptographer), then I can already tell you the result.
Your scheme is hopelessly flawed, and can be broken by even undergraduate level cryptographers. Not that your scheme will ever encrypt anything so valuable as to be worth the time to crack.
Cryptography is NOT for the inexperienced. More than any other discipline, it constantly builds on previous knowledge. There are no "revolutions" in crypto, and a new-and-novel-scheme is NEVER recommended.
If you are writing a program for fun or to learn about encryption, great, explore and learn. If you are using a major language there are lots of available libraries free to use that will do encryption properly for you. I'd highly recommend leveraging one of these libraries if you are doing this as a professional endeavor.
If you are looking to learn more about encryption start with the book Applied Cryptography from Bruce Schneier its old but will give you a good base understanding and you can find newer texts from him or other reputable authors to build upon that knowledge. He has a site at http://www.schneier.com/
I can't agree enough with @abelenky and @MegaCraig: if you actually care about securing data, creating your own encryption scheme is a horrible idea.
If you want to learn, you may want to start with the Wikipedia article on cryptanalysis.
If you follow up with the articles on various types of cryptanalysis, you can often find links to tools that will perform that specific type of cryptanalysis, e.g., this tool for doing frequency analysis.
Bruce Schneier has written well on this very subject. Please read Memo to the Amateur Cipher Designer.
You would do well to get his book Applied Cryptography, read his blog where he occasionally points out flawed schemes, read cryptanalysis papers to see what an a real attack looks like. Attacks usually rely on mathematical properties of the algorithm.
And that is just Schneier. There are many other cryptologists you could learn from. Read the bibliography of Schneier's book for links.