Add unit test

Author: chansuke

src/env_var.rs

@@ -47,3 +47,52 @@ pub fn inc(name: &str, cmd: &mut Command) {
 
     cmd.env(name, (old_value + 1).to_string());
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::currentprocess;
+    use crate::test::{with_saved_path, Env};
+
+    use std::collections::HashMap;
+    use std::ffi::{OsStr, OsString};
+
+    #[test]
+    fn prepent_unique_path() {
+        let mut vars = HashMap::new();
+        vars.env("PATH", "/home/a/.cargo/bin:/home/b/.cargo/bin");
+        let tp = Box::new(currentprocess::TestProcess {
+            vars,
+            ..Default::default()
+        });
+        with_saved_path(&|| {
+            currentprocess::with(tp.clone(), || {
+                let mut path_entries = vec![];
+                let mut cmd = Command::new("test");
+
+                // duplicated PATH.
+                let a = OsString::from("/home/a/.cargo/bin");
+                let path_a = PathBuf::from(a);
+                path_entries.push(path_a);
+                // unique PATH.
+                let z = OsString::from("/home/z/.cargo/bin");
+                let path_z = PathBuf::from(z);
+                path_entries.push(path_z);
+
+                prepend_path("PATH", path_entries, &mut cmd);
+
+                let envs: Vec<(&OsStr, Option<&OsStr>)> = cmd.get_envs().collect();
+
+                assert_eq!(
+                    envs,
+                    &[(
+                        OsStr::new("PATH"),
+                        Some(OsStr::new(
+                            "/home/a/.cargo/bin:/home/b/.cargo/bin:/home/z/.cargo/bin"
+                        ))
+                    ),]
+                );
+            });
+        });
+    }
+}

src/lib.rs

@@ -1,3 +1,4 @@
+#![feature(command_access)]
 #![deny(rust_2018_idioms)]
 #![allow(
     clippy::too_many_arguments,