require_full_match mode always fails with matching snapshots

[dspicher]

What happened?

When I run INSTA_REQUIRE_FULL_MATCH=1 cargo test on a dummy snapshot test case, it fails with the following output:

Output

$ INSTA_REQUIRE_FULL_MATCH=1 cargo t
   Compiling insta-tests v0.1.0 (/home/dominik/purgable/insta-tests)
    Finished test [unoptimized + debuginfo] target(s) in 0.44s
     Running unittests src/lib.rs (target/debug/deps/insta_tests-3c106da6b8f1533f)

running 1 test
test tests::test_insta ... FAILED

failures:

---- tests::test_insta stdout ----
━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Snapshot Summary ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
Snapshot file: src/snapshots/insta_tests__tests__insta.snap
Snapshot: insta
Source: src/lib.rs:5
──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
Expression: 1 + 1
──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
-old snapshot
+new results
────────────┬─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
          - │ snapshots are matching
────────────┴─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
To update snapshots run `cargo insta review`
Stopped on the first failure. Run `cargo insta test` to run all snapshots.
thread 'tests::test_insta' panicked at .../.cargo/registry/src/index.crates.io-6f17d22bba15001f/insta-1.38.0/src/runtime.rs:563:9:
snapshot assertion for 'insta' failed in line 5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace


failures:
    tests::test_insta

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.06s

error: test failed, to rerun pass `--lib`

This is even though the expected output, as well as the expression match the snapshot file.

The normal cargo test snapshot test passes as expected.

Reproduction steps

1. Run INSTA_REQUIRE_FULL_MATCH=1 cargo test on this minimal reproducing example.

Insta Version

cargo-insta 1.38.0

rustc Version

rustc 1.77.2 (25ef9e3d8 2024-04-09)

What did you expect?

The test should pass.

[max-sixty]

This is indeed a bug.

We can work around it temporarily by changing the test name to something that insta doesn't change:

diff --git a/src/lib.rs b/src/lib.rs
index 3f262aa..b23d00e 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,7 +1,7 @@
 #[cfg(test)]
 mod tests {
     #[test]
-    fn test_insta() {
-        insta::assert_json_snapshot!(1+1);
+    fn insta() {
+        insta::assert_json_snapshot!(1 + 1);
     }
 }

...since it's caused by the name of the snapshot name being truncated, and so the metadata not matching.

We can fix it by aligning name truncation to the metadata comparison.

---- tests::test_insta stdout ----
[/Users/maximilian/workspace/insta/insta/src/runtime.rs:674:17] &x = Snapshot {
    module_name: "insta_tests",
    snapshot_name: Some(
        "tests__insta",
    ),
    metadata: MetaData {
        source: Some(
            "src/lib.rs",
        ),
        assertion_line: None,
        description: None,
        expression: Some(
            "1 + 1",
        ),
        info: None,
        input_file: None,
    },
    snapshot: SnapshotContents(
        "2",
    ),
}
[/Users/maximilian/workspace/insta/insta/src/runtime.rs:674:17] &new_snapshot = Snapshot {
    module_name: "insta_tests__tests",
    snapshot_name: Some(
        "insta",
    ),
    metadata: MetaData {
        source: Some(
            "src/lib.rs",
        ),
        assertion_line: Some(
            5,
        ),
        description: None,
        expression: Some(
            "1 + 1",
        ),
        info: None,
        input_file: None,
    },
    snapshot: SnapshotContents(
        "2",
    ),
}

[max-sixty]

There are a couple of other issues when calling cargo test rather than cargo insta test. I'll come back to this hopefully later this week