feat(test): use snapshots for testing

.cargo/config.toml

@@ -0,0 +1,3 @@
+[env]
+# insta writes multi-line snapshot metadata as unquoted literal blocks
+INSTA_YAML_BLOCK_STYLE = "1"

.gitignore

@@ -10,3 +10,6 @@ pkg/aur/.SRCINFO
 
 # dummy dir to test org behaviour
 toss/
+
+# don't commit pending snapshots
+*.snap.new

README.org

@@ -45,3 +45,32 @@ cargo install org-rust
 *** Development
 
 Refer to the [[./docs][documentation]] for developer-specific information & syntax-progress.
+
+
+** Testing
+
+The parser and exporter rely on snapshot tests built on [[https://insta.rs/][insta]].
+A snapshot test processes a small input and compares the output against a stored snapshot (~.snap~) in ~crates/<crate>/snapshots/~.
+Parser tests compare against the output ~Parser::render_tree()~ to ensure stability.
+Exporter snapshot tests are handled [[https://insta.rs/docs/quickstart/#inline-snapshots][inline]].
+
+*** Snapshot workflow
+
+After making a change, run the tests as usual with ~cargo test --workspace~.
+If a snapshot doesn't match (or doesn't exist yet), the test fails and ~insta~ generates a pending snapshot as a ~.snap.new~ file.
+
+Read the diff to verify correctness. Optionally, [[https://insta.rs/docs/cli/][cargo-insta]] offers a convenience tool for this:
+
+#+begin_src bash
+cargo insta review
+#+end_src
+
+If every change is intended, ~INSTA_UPDATE=always cargo test --workspace~ accepts them all at once, overwriting the stored snapshots directly.
+
+*** Adding a test
+
+The snapshot is named after the module path and test name.
+
+1. Run ~cargo test~. The new test fails and writes a ~.snap.new~.
+2. Check, then accept it with ~cargo insta review~ / ~cargo insta accept~ or just do it manually.
+3. Re-run ~cargo test~, then commit the new ~.snap~ file.

crates/org-exporter/Cargo.toml

@@ -19,4 +19,5 @@ phf = {version = "0.11.1", features = ["macros"]}
 thiserror = "1.0.63"
 
 [dev-dependencies]
+insta = "1.48.0"
 pretty_assertions = "1.3.0"