Add section on analysis tests

Author: nojaf

analysis/README.md

@@ -24,3 +24,28 @@ dune exec -- rescript-editor-analysis --help
 ## History
 
 This project is based on a fork of [Reason Language Server](https://github.com/jaredly/reason-language-server).
+
+## Tests
+
+The tests in the `analysis/test` folder are based on the `./rescript-editor-analysis.exe test` command. This special subcommand processes a file and executes specific editor analysis functionality based on special syntax found in code comments.
+
+Consider the following code:
+
+```res
+let a = 5
+// a.
+//   ^com
+```
+
+After building the ReScript project (**⚠️ this is a requirement**), you can execute `./rescript-editor-analysis.exe test Sample.res`, and completion will be executed for the cursor position indicated by `^`. The `com` directive requests completion. To see other commands, check out the pattern match in `test` in [Commands.ml](./src/Commands.ml).
+
+Here’s how it works: once a command is found in a comment, a copy of the source file is created inside a temporary directory, where the line above `^com` is uncommented. The corresponding analysis functionality is then processed, typically with `~debug:true`. With debug enabled, code paths like
+
+```ml
+if Debug.verbose () then
+      print_endline "[complete_typed_value]--> Tfunction #other";
+```
+
+will print to stdout. This is helpful for observing what occurs during the analysis.
+
+When you run `make test` (from the `analysis/tests` folder), `./rescript-editor-analysis.exe test <file>` will be executed for each `*.res` file in `analysis/tests/src`. The stdout will be compared to the corresponding `analysis/tests/src/expected` file. If `git diff` indicates changes, `make test` will fail, as these differences might be unintentional.