Introduce constant dist dirs for testing

* Rename setup() to test() as it only returns after the test has happened.
* Separate tracking the mutable dist servers from the new const dist server
* Permit starting a test with no dist server
* add with_scenario to construct a specific dist server on-demand, but also cache it for other tests
* Migrate cli-exact to use with_scenario
* Remove some stale no longer relvant end of test checks
* Cached dist servers are generated new per test run for now, and are
  unique per test binary. They leak at the end of the test, but aren't
  very large. Clean your target :).
* Simplify many tests that had unnecessary work in them (work that wasn't being tested)

Author: rbtcollins

CONTRIBUTING.md

@@ -252,7 +252,7 @@ stack backtrace:
    8: core::panicking::panic_fmt
              at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\/src\libcore\panicking.rs:85
    9: core::result::unwrap_failed
-  10: cli_v1::mock::clitools::setup
+  10: cli_v1::mock::clitools::test
   11: alloc::boxed::{{impl}}::call_once<(),FnOnce<()>>
              at /rustc/de02101e6d949c4a9040211e9ce8c488a997497e\src\liballoc\boxed.rs:746
   12: panic_unwind::__rust_maybe_catch_panic

Cargo.lock

@@ -109,6 +109,8 @@ version = "0.3"
 
 [dev-dependencies]
 walkdir = "2"
+once_cell = "1.17.0"
+enum-map = "2.4.2"
 
 [build-dependencies]
 lazy_static = "1"

Cargo.toml

@@ -45,20 +45,52 @@ impl Env for HashMap<String, String> {
     }
 }
 
-/// Returns a tempdir for running tests in
-pub fn test_dir() -> io::Result<tempfile::TempDir> {
+/// The path to a dir for this test binaries state
+fn exe_test_dir() -> io::Result<PathBuf> {
     let current_exe_path = env::current_exe().unwrap();
     let mut exe_dir = current_exe_path.parent().unwrap();
     if exe_dir.ends_with("deps") {
         exe_dir = exe_dir.parent().unwrap();
     }
-    let test_dir = exe_dir.parent().unwrap().join("tests");
+    Ok(exe_dir.parent().unwrap().to_owned())
+}
+
+/// Returns a tempdir for running tests in
+pub fn test_dir() -> io::Result<tempfile::TempDir> {
+    let exe_dir = exe_test_dir()?;
+    let test_dir = exe_dir.join("tests");
     fs::create_dir_all(&test_dir).unwrap();
     tempfile::Builder::new()
         .prefix("running-test-")
         .tempdir_in(test_dir)
 }
 
+/// Returns a directory for storing immutable distributions in
+pub fn const_dist_dir() -> io::Result<tempfile::TempDir> {
+    // TODO: do something smart, like managing garbage collection or something.
+    let exe_dir = exe_test_dir()?;
+    let dists_dir = exe_dir.join("dists");
+    fs::create_dir_all(&dists_dir)?;
+    let current_exe = env::current_exe().unwrap();
+    let current_exe_name = current_exe.file_name().unwrap();
+    tempfile::Builder::new()
+        .prefix(&format!(
+            "dist-for-{}-",
+            Path::new(current_exe_name).display()
+        ))
+        .tempdir_in(dists_dir)
+}
+
+/// Returns a tempdir for storing test-scoped distributions in
+pub fn test_dist_dir() -> io::Result<tempfile::TempDir> {
+    let exe_dir = exe_test_dir()?;
+    let test_dir = exe_dir.join("tests");
+    fs::create_dir_all(&test_dir).unwrap();
+    tempfile::Builder::new()
+        .prefix("test-dist-dir-")
+        .tempdir_in(test_dir)
+}
+
 /// Makes persistent unique directory inside path.
 ///
 /// Should only be used with path=a tempdir that will be cleaned up, as the