Added tests

tests/README.md

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+# Tests for osxphotos #
+
+## Running Tests ##
+Tests require pytest:
+`pip install pytest`
+
+To run the tests, do the following from the main source folder:
+`python -m pytest tests/`
+
+Running the tests this way allows the library to be tested without installing it.
+
+## Attribution ##
+These tests utilize a test Photos library. The test library is populated with photos from [flickr](https://www.flickr.com).  All images used are licensed under Creative Commons 2.0 Attribution [license](https://creativecommons.org/licenses/by/2.0/).  
+
+Images used from:
+- [Jeff Hitchcock](https://www.flickr.com/photos/arbron/48353451872/)
+- [Carlos Montesdeoca](https://www.flickr.com/photos/carlosmontesdeocastudio)
+- [Rydale Clothing](https://www.flickr.com/photos/rydaleclothing)
+- [Marco Verch](https://www.flickr.com/photos/30478819@N08/48228222317/)
+
+