Add some extra diff-based testing utilities

These will be used in the imports tests to allow snapshotting diffs of the
relevant imports.lock files.

Cargo.toml

@@ -57,3 +57,4 @@ features = [
 
 [dev-dependencies]
 insta = "1.15.0"
+similar = "2.1.0"

src/storage.rs

@@ -273,6 +273,26 @@ impl Store {
         Ok(())
     }
 
+    /// Mock `commit`. Returns the serialized value for each file in the store.
+    /// Doesn't take `self` by value so that it can continue to be used.
+    #[cfg(test)]
+    pub fn mock_commit(&self) -> SortedMap<String, String> {
+        let mut audits = Vec::new();
+        let mut config = Vec::new();
+        let mut imports = Vec::new();
+        store_audits(&mut audits, self.audits.clone()).unwrap();
+        store_config(&mut config, self.config.clone()).unwrap();
+        store_imports(&mut imports, self.imports.clone()).unwrap();
+
+        [
+            (AUDITS_TOML.to_owned(), String::from_utf8(audits).unwrap()),
+            (CONFIG_TOML.to_owned(), String::from_utf8(config).unwrap()),
+            (IMPORTS_LOCK.to_owned(), String::from_utf8(imports).unwrap()),
+        ]
+        .into_iter()
+        .collect()
+    }
+
     /// Validate the store's integrity
     #[allow(clippy::for_kv_map)]
     pub fn validate(&self) -> Result<(), StoreValidateErrors> {

src/tests/mod.rs

@@ -14,7 +14,7 @@ use crate::{
     editor::Editor,
     format::{
         AuditKind, CriteriaName, CriteriaStr, Delta, DependencyCriteria, FastMap, MetaConfig,
-        PackageName, PackageStr, PolicyEntry, VersionReq, SAFE_TO_DEPLOY, SAFE_TO_RUN,
+        PackageName, PackageStr, PolicyEntry, SortedSet, VersionReq, SAFE_TO_DEPLOY, SAFE_TO_RUN,
     },
     init_files,
     out::Out,
@@ -1152,6 +1152,32 @@ impl Out for BasicTestOutput {
     }
 }
 
+/// Format a diff between the old and new strings for reporting.
+fn generate_diff(old: &str, new: &str) -> String {
+    similar::utils::diff_lines(similar::Algorithm::Myers, old, new)
+        .into_iter()
+        .map(|(tag, line)| format!("{}{}", tag, line))
+        .collect()
+}
+
+/// Generate a diff between two values returned from `Store::mock_commit`.
+fn diff_store_commits(old: &SortedMap<String, String>, new: &SortedMap<String, String>) -> String {
+    use std::fmt::Write;
+    let mut result = String::new();
+    let keys = old.keys().chain(new.keys()).collect::<SortedSet<&String>>();
+    for key in keys {
+        let old = old.get(key).map(|s| &s[..]).unwrap_or("");
+        let new = new.get(key).map(|s| &s[..]).unwrap_or("");
+        if old == new {
+            writeln!(&mut result, "{key}: (unchanged)").unwrap();
+            continue;
+        }
+        let diff = generate_diff(old, new);
+        writeln!(&mut result, "{key}:\n{diff}").unwrap();
+    }
+    result
+}
+
 // TESTING BACKLOG:
 //
 // * custom policies