I can’t give you any markers, not to mention the RoR to Symfony migration guide, but I can tell you how I approach it. Remember, just because two applications use the same design pattern, their implementation may be different, so you probably have to adjust a lot of code, despite any common idioms.
Assuming the RoR project is covered by UnitTests, I would start porting all tests to PHPUnit. Start with functional tests. Since the problem area does not change when porting, they should be the same as in RoR. Leave them blank if you cannot immediately implement them. The main thing is to describe what the application should do at the end.
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