tests: Move 'mocked pagers' utils to separate file

tests/utils/mocked_pagers.rs

@@ -0,0 +1,69 @@
+use assert_cmd::Command;
+use predicates::prelude::predicate;
+use std::env;
+use std::path::{Path, PathBuf};
+
+/// For some tests we want mocked versions of some pagers
+/// This fn returns the absolute path to the directory with these mocked pagers
+fn get_mocked_pagers_dir() -> PathBuf {
+    let cargo_manifest_dir = env::var("CARGO_MANIFEST_DIR").expect("Missing CARGO_MANIFEST_DIR");
+    Path::new(&cargo_manifest_dir)
+        .join("tests")
+        .join("mocked-pagers")
+}
+
+/// On Unix: 'most' -> 'most'
+/// On Windows: 'most' -> 'most.bat'
+pub fn from(base: &str) -> String {
+    if cfg!(windows) {
+        format!("{}.bat", base)
+    } else {
+        String::from(base)
+    }
+}
+
+/// Prepends a directory to the PATH environment variable
+/// Returns the original value for later restoration
+fn prepend_dir_to_path_env_var(dir: PathBuf) -> String {
+    // Get current PATH
+    let original_path = env::var("PATH").expect("No PATH?!");
+
+    // Add the new dir first
+    let mut split_paths = env::split_paths(&original_path).collect::<Vec<_>>();
+    split_paths.insert(0, dir);
+
+    // Set PATH with the new dir
+    let new_path = env::join_paths(split_paths).expect("Failed to join paths");
+    env::set_var("PATH", new_path);
+
+    // Return the original value for later restoration of it
+    original_path
+}
+
+/// Helper to restore the value of PATH
+fn restore_path(original_path: String) {
+    env::set_var("PATH", original_path);
+}
+
+/// Allows test to run that require our mocked versions of 'more' and 'most'
+/// in PATH. Temporarily changes PATH while the test code runs, and then restore it
+/// to avoid pollution of global state
+pub fn with_mocked_versions_of_more_and_most_in_path(actual_test: fn()) {
+    let original_path = prepend_dir_to_path_env_var(get_mocked_pagers_dir());
+
+    // Make sure our own variants of 'more' and 'most' are used
+    Command::new(from("more"))
+        .assert()
+        .success()
+        .stdout(predicate::str::contains("I am more"));
+    Command::new(from("most"))
+        .assert()
+        .success()
+        .stdout(predicate::str::contains("I am most"));
+
+    // Now run the actual test
+    actual_test();
+
+    // Make sure to restore PATH since it is global state
+    restore_path(original_path);
+}