(WIP) use rstest to parameterize test cases

Cargo.toml

@@ -60,6 +60,7 @@ ctrlc = { version = "3.1.1", features = ["termination"] }
 [dev-dependencies]
 clap_complete = "=4.5.48"
 pretty_assertions = "1.0.0"
+rstest = "0.26.1"
 temptree = "0.2.0"
 which = "8.0.0"
 

TEST_REFACTOR.md

@@ -0,0 +1,79 @@
+# Test Refactoring Plan
+
+## Goal
+
+Reduce the number of separate tests and verbosity while still exercising the code in the same way.
+
+## Strategies
+
+### 1. Parameterized / data-driven tests (biggest win)
+
+Many tests differ only in input/output data. Use loop-in-a-single-test:
+
+```rust
+#[test]
+fn string_functions() {
+  for (func, input, expected) in [
+    ("uppercase", "bar", "BAR"),
+    ("lowercase", "BAR", "bar"),
+    // ...
+  ] {
+    Test::new()
+      .justfile(&format!("foo:\n  echo {{{{ {func}('{input}') }}}}"))
+      .stdout(&format!("{expected}\n"))
+      .stderr(&format!("echo {expected}\n"))
+      .success();
+  }
+}
+```
+
+Applies to:
+- String function tests in `functions.rs` (~20+ tests → 1-2)
+- Path function error tests in `functions.rs` (~6+ tests → 1)
+- Case conversion tests throughout
+
+### 2. Merge tests that exercise the same feature with slight variations
+
+Tests like `test_os_arch_functions_in_interpolation`, `_in_expression`, and `_in_default` repeat identical stdout/stderr assertions — only the justfile differs. These could be a single test with a loop over justfile variants.
+
+Similarly in `options.rs`, tests sharing the `LONG_SHORT` constant justfile could be one test that runs multiple arg combinations.
+
+### 3. Macro-generated test functions (preserves individual test names)
+
+For cases where individual test names are important:
+
+```rust
+macro_rules! test_function {
+  ($name:ident, $func:expr, $input:expr, $expected:expr) => {
+    #[test]
+    fn $name() {
+      Test::new()
+        .justfile(&format!("foo:\n  echo {{{{ {}('{}') }}}}", $func, $input))
+        .stdout(&format!("{}\n", $expected))
+        .stderr(&format!("echo {}\n", $expected))
+        .success();
+    }
+  };
+}
+
+test_function!(uppercase, "uppercase", "bar", "BAR");
+test_function!(lowercase, "lowercase", "BAR", "bar");
+```
+
+### 4. Consolidate multi-assertion unit tests
+
+Group related assertions into fewer test functions, similar to what the inline `#[cfg(test)]` unit tests already do.
+
+### 5. Extract shared error-format helpers
+
+The "broken function" error tests construct error messages with the same format. A helper function would cut significant duplication.
+
+## Priority Areas
+
+| Area | Current tests | Could become | Technique |
+|------|--------------|-------------|-----------|
+| String functions (`functions.rs`) | ~20 | 1-2 | Data-driven loop |
+| Path error tests (`functions.rs`) | ~6 | 1 | Data-driven loop |
+| OS/arch placement tests | 3 | 1 | Loop over justfile variants |
+| Options arg-passing tests | ~10 | 2-3 | Merge by shared justfile |
+| `misc.rs` listing variants | many groups of 3-5 | fewer | Merge closely related ones |