Allow tester to compare directories

The compare command now accepts directories as arguments and will
automatically use the latest.json file from those directories.
This maintains backward compatibility with explicit file paths.

Author: HalidOdat

CONTRIBUTING.md

@@ -91,6 +91,33 @@ be more readable if you disable parallelism with the `-d` flag. All together it
 cargo run --release --bin boa_tester -- run -vv -d -s test/language/types/number 2> error.log
 ```
 
+To save test results for later comparison, use the `-o` flag to specify an output directory:
+
+```shell
+cargo run --release --bin boa_tester -- run -o ./test-results
+```
+
+### Comparing Test Results
+
+You can compare two test suite runs to see what changed:
+
+```shell
+cargo run --release --bin boa_tester -- compare <base-results> <new-results>
+```
+
+Both arguments can be either result files (e.g., `latest.json`) or directories containing test results.
+When directories are provided, the tester automatically uses the `latest.json` file from each directory.
+
+For example:
+
+```shell
+# Compare using directories
+cargo run --release --bin boa_tester -- compare ./test-results-main ./test-results-feature
+
+# Compare using explicit files
+cargo run --release --bin boa_tester -- compare ./test-results-main/latest.json ./test-results-feature/latest.json
+```
+
 ## Documentation
 
 To build the development documentation, run:

tests/tester/src/results.rs

@@ -170,13 +170,26 @@ fn get_test262_commit(test262_path: &Path) -> Result<Box<str>> {
 /// Compares the results of two test suite runs.
 #[allow(clippy::cast_possible_wrap)]
 pub(crate) fn compare_results(base: &Path, new: &Path, markdown: bool) -> Result<()> {
+    // If the path is a directory, use latest.json from that directory
+    let base_path = if base.is_dir() {
+        base.join(LATEST_FILE_NAME)
+    } else {
+        base.to_path_buf()
+    };
+
+    let new_path = if new.is_dir() {
+        new.join(LATEST_FILE_NAME)
+    } else {
+        new.to_path_buf()
+    };
+
     let base_results: ResultInfo = serde_json::from_reader(BufReader::new(
-        fs::File::open(base).wrap_err("could not open the base results file")?,
+        fs::File::open(&base_path).wrap_err("could not open the base results file")?,
     ))
     .wrap_err("could not read the base results")?;
 
     let new_results: ResultInfo = serde_json::from_reader(BufReader::new(
-        fs::File::open(new).wrap_err("could not open the new results file")?,
+        fs::File::open(&new_path).wrap_err("could not open the new results file")?,
     ))
     .wrap_err("could not read the new results")?;