Added initial testing documentation

tests/README.txt

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+This document describes the testing done in the OSIPI TF2.4 IVIM repository
+
+
+-- Outline --
+1. Testing philosophy
+2. Testing structure
+3. Testing results
+
+
+
+-- Testing philosophy --
+Testing is integral to the repository.
+There are many different contributions from many different people and only through diligent testing can they all be ensured to work correctly together.
+There are 3 major types of tests we conduct.
+1. Requirements
+    - Which are required to pass
+    - All algorithms have the same requirements
+    - E.g. bounds honored, code runs reasonably
+2. Expectations
+    - Considered warnings
+    - Should not necessarily prevent a merge
+    - Should cover performance changes
+    - E.g. performance changes
+3. Performance
+    - The accuracy of the results
+    - The speed of the generated results
+
+-- Testing structure --
+* The testing is controlled in several places.
+* The testing itself is done with pytest which parses files for "test_" and runs the appropriate tests.
+* The pytest testing can be done on your own machine by running "python -m pytest".
+** This is configured with pytests.ini and conftest.py
+* Testing on github is controlled by the github actions which are in the workflows folder.
+* Each workflow performs a series of tests, and is defined by the yml file.
+* Each workflow can run at specified times and with specified outputs.
+* Currently the major testing workflows are unit_test.yml and analysis.yml.
+* The unit_test workflow is done frequently and is relativly fast and does some basic algorithm testing.
+* The analysis workflow is done more infrequently with merges to the main branch and does more Expecation testing.
+
+
+-- Testing results --
+The test results are written to several files, most notably an xml file for machine parsing, and a web page for code coverage.
+The "analysis" tests are written to a csv file as well.