Isolate trycmd tests from environment

Author: rbtcollins

tests/suite/cli_ui.rs

@@ -5,12 +5,16 @@ use rustup_macros::integration_test as test;
 #[test]
 fn rustup_ui_doc_text_tests() {
     let t = trycmd::TestCases::new();
+    let home = tempfile::TempDir::new().unwrap();
     let rustup_init = trycmd::cargo::cargo_bin("rustup-init");
     let rustup = trycmd::cargo::cargo_bin("rustup");
     // Copy rustup-init to rustup so that the tests can run it.
     fs::copy(rustup_init, &rustup).unwrap();
     t.register_bin("rustup", &rustup);
     t.case("tests/suite/cli-ui/rustup/*.toml");
+    // once installed rustup asserts the presence of ~/.rustup/settings.toml if
+    // Config is instantiated.
+    t.env("HOME", home.path().to_string_lossy());
     #[cfg(target_os = "windows")]
     {
         // On windows, we don't have man command, so skip the test.