Organize test code better

tests/unit/env.rs

@@ -0,0 +1,37 @@
+use super::*;
+
+#[test]
+fn keepenv_emits_setenv_for_present_key() {
+    let parent = vec![("XDG_RUNTIME_DIR".into(), "/run/user/1000".into())];
+    let args = keepenv_args(&["XDG_RUNTIME_DIR".into()], &parent);
+    assert_eq!(args, vec!["--setenv", "XDG_RUNTIME_DIR", "/run/user/1000"]);
+}
+
+#[test]
+fn keepenv_skips_absent_keys() {
+    let parent = vec![("HOME".into(), "/home/me".into())];
+    let args = keepenv_args(&["XDG_RUNTIME_DIR".into()], &parent);
+    assert!(args.is_empty());
+}
+
+#[test]
+fn keepenv_preserves_caller_key_order() {
+    let parent = vec![
+        ("B".into(), "2".into()),
+        ("A".into(), "1".into()),
+        ("C".into(), "3".into()),
+    ];
+    let args = keepenv_args(&["A".into(), "B".into(), "C".into()], &parent);
+    assert_eq!(
+        args,
+        vec![
+            "--setenv", "A", "1", "--setenv", "B", "2", "--setenv", "C", "3"
+        ]
+    );
+}
+
+#[test]
+fn keepenv_empty_keys_yields_nothing() {
+    let parent = vec![("A".into(), "1".into())];
+    assert!(keepenv_args(&[], &parent).is_empty());
+}