[coverage-improver] Cover MockFs stub trait methods in discovery.rs

[TheLarkInn]

What branch was uncovered

crates/libaipm/src/make/discovery.rs — the MockFs test helper's Fs
trait-implementation stubs (create_dir_all, write_file, read_to_string,
read_dir, lines 82–96) were never exercised by any existing test. These
methods exist only to satisfy the Fs trait bound for MockFs, but
find_marketplace/has_any_engine_marketplace only ever call exists, so
the other four methods' bodies (and their branch outcomes, e.g. the Err
path in read_to_string) were unreachable through the existing test suite,
dragging the file's branch coverage down to 64.71%.

What scenario the new test covers

Added mock_fs_stub_methods_return_expected_defaults, which directly calls
create_dir_all, write_file, read_to_string, and read_dir on a fresh
MockFs instance and asserts their documented stub behavior: the first two
return Ok(()), read_to_string returns an Err (since it always reports
"not used"), and read_dir returns an empty Vec.

Before/after branch coverage

• discovery.rs branch coverage: 64.71% → 88.89%
• Workspace TOTAL branch coverage: 90.64% → 90.72%

Test code added

/// Covers the unused-by-`find_marketplace` `Fs` trait methods on
/// `MockFs`. These stubs exist only to satisfy the `Fs` trait bound and
/// are never reached through `find_marketplace`/`has_any_engine_marketplace`,
/// so exercise them directly.
#[test]
fn mock_fs_stub_methods_return_expected_defaults() {
    let fs = MockFs::new();
    let path = Path::new("/project/.ai");

    assert!(fs.create_dir_all(path).is_ok());
    assert!(fs.write_file(path, b"content").is_ok());
    assert!(fs.read_to_string(path).is_err());
    assert_eq!(fs.read_dir(path).unwrap_or_default().len(), 0);
}

Verification

• cargo build --workspace ✅
• cargo test --workspace ✅ (all 6 discovery tests pass)
• cargo fmt --check ✅
• cargo clippy --workspace -- -D warnings — pre-existing failures unrelated
  to this change (2 manual_is_variant_and lints in resolver/mod.rs and
  security.rs from the Rust 1.98.0 toolchain bump, already being addressed
  in PR fix(clippy): use Result::is_ok_and for Rust 1.98.0 manual_is_variant_and lint #1631); no clippy issues in the modified file.

Generated by Coverage Improver · auto · 109.2 AIC · ⌖ 8.3 AIC · ⊞ 13.1K · ◷

---

Note

This was originally intended as a pull request, but PR creation failed. The changes have been pushed to the branch coverage-improver/discovery-mockfs-stub-methods-c1bd38748bdcd928.

Original error: ERR_API: [2026-08-21T12:57:49.430Z] create pull request in TheLarkInn/aipm failed (attempt 1)

Original error: Resource not accessible by personal access token - https://docs.github.com/rest/pulls/pulls#create-a-pull-request
Retryable: false
Suggestion: This error cannot be resolved by retrying. Please check the error details and fix the underlying issue.

To create the pull request manually:

gh pr create --title "[coverage-improver] Cover MockFs stub trait methods in discovery.rs" --base main --head coverage-improver/discovery-mockfs-stub-methods-c1bd38748bdcd928 --repo TheLarkInn/aipm

Show patch (39 lines)

From a3859308bcacc456a1e4276928fe51bc6c071e70 Mon Sep 17 00:00:00 2001
X-GH-AW-Base-Commit: 6d3368da0e97be67cb075dba37b9b384df816358
From: "github-actions[bot]" <github-actions[bot]@users.noreply.github.com>
Date: Fri, 21 Aug 2026 12:53:46 +0000
Subject: [PATCH] test(discovery): cover MockFs stub trait method branches

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
---
 crates/libaipm/src/make/discovery.rs | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/crates/libaipm/src/make/discovery.rs b/crates/libaipm/src/make/discovery.rs
index 9245688..6c977e8 100644
--- a/crates/libaipm/src/make/discovery.rs
+++ b/crates/libaipm/src/make/discovery.rs
@@ -149,4 +149,19 @@ mod tests {
         let result = find_marketplace(Path::new("/"), &fs);
         assert!(result.is_err());
     }
+
+    /// Covers the unused-by-`find_marketplace` `Fs` trait methods on
+    /// `MockFs`. These stubs exist only to satisfy the `Fs` trait bound and
+    /// are never reached through `find_marketplace`/`has_any_engine_marketplace`,
+    /// so exercise them directly.
+    #[test]
+    fn mock_fs_stub_methods_return_expected_defaults() {
+        let fs = MockFs::new();
+        let path = Path::new("/project/.ai");
+
+        assert!(fs.create_dir_all(path).is_ok());
+        assert!(fs.write_file(path, b"content").is_ok());
+        assert!(fs.read_to_string(path).is_err());
+        assert_eq!(fs.read_dir(path).unwrap_or_default().len(), 0);
+    }
 }
-- 
2.54.0