+the more comprehensive wrapper file used to run binaries is called
+`pypowersim`.
+
+## `-->` START HERE `<--` Run `ISACaller` unit tests first!
+
+TODO: Document tutorial.
+
+Since `pypowersim` is much more involved (as it requires PC, register setup,
+etc.), it is *strogly* encouraged to first write a basic unit test involving
+the `ISACaller` class.
+
+### Find appropriate umbrella `test_caller_[FUNCTION].py` class
+
+The directory `openpower-isa/src/openpower/decoder/isa/` contains a set of files
+for running unit tests using pytest. If adding tests for a new category, a new
+umbrella will need to be created.
+
+The umbrella file has name of the form `test_caller_[FUNCTION].py`.
+For example of the ALU test caller, see
+[`test_caller_alu.py`](https://git.libre-soc.org/?p=openpower-isa.git;a=blob;f=src/openpower/decoder/isa/test_caller_alu.py;hb=HEAD).
+
+It's suggested to copy the contents of an existing test caller file.
+
+### Write unit tests under the `src/openpower/test/[FUNCTION]/` directory
+
+Once a test caller class exists, the actual tests reside under the
+`src/openpower/test/[FUNCTION]/` directory. For example of the ALU tests, see
+[alu_cases.py](https://git.libre-soc.org/?p=openpower-isa.git;a=blob;f=src/openpower/test/alu/alu_cases.py;hb=HEAD)
+
+Copy an existing file when writing new tests, which should gradually teach you
+how to use the `ISACaller` class.
+
+### Example of new test - system call instructions
+
+