Add test to ensure resolution of #3418

Author: rami3l

tests/suite/cli_v2.rs

@@ -1034,6 +1034,27 @@ fn update_unavailable_std() {
     });
 }
 
+#[test]
+fn add_missing_component() {
+    setup(&|config| {
+        make_component_unavailable(config, "rls-preview", &this_host_triple());
+        config.expect_ok(&["rustup", "toolchain", "add", "nightly"]);
+        config.expect_err(
+            &["rustup", "component", "add", "rls-preview"],
+            for_host!(
+                "component 'rls' for target '{0}' is unavailable for download for channel 'nightly'\n\
+                Sometimes not all components are available in any given nightly."
+            ),
+        );
+        // Make sure the following pattern does not match,
+        // thus addressing https://github.com/rust-lang/rustup/issues/3418.
+        config.expect_not_stderr_err(
+            &["rustup", "component", "add", "rls-preview"],
+            "If you don't need the component, you can remove it with:",
+        );
+    });
+}
+
 #[test]
 fn add_missing_component_toolchain() {
     setup(&|config| {