Add a test for the cargo tree --all warning.

Author: jneem

tests/testsuite/cargo_tree/dupe/mod.rs

@@ -2,6 +2,7 @@ use crate::prelude::*;
 use cargo_test_support::file;
 use cargo_test_support::project;
 use cargo_test_support::registry::Package;
+use cargo_test_support::str;
 
 #[cargo_test]
 fn case() {
@@ -34,3 +35,33 @@ fn case() {
         .stdout_eq(file!["stdout.term.svg"])
         .stderr_eq(file!["stderr.term.svg"]);
 }
+
+#[cargo_test]
+fn all_flag() {
+    Package::new("a", "1.0.0").dep("b", "1.0").publish();
+    Package::new("b", "1.0.0").dep("c", "1.0").publish();
+    Package::new("c", "1.0.0").publish();
+
+    let p = project()
+        .file(
+            "Cargo.toml",
+            r#"
+            [package]
+            name = "foo"
+            version = "0.1.0"
+
+            [dependencies]
+            a = "1.0"
+            b = "1.0"
+            "#,
+        )
+        .file("src/lib.rs", "")
+        .file("build.rs", "fn main() {}")
+        .build();
+
+    p.cargo("tree --all").with_stderr_data(str![[r#"
+[WARNING] The `cargo tree` --all flag has been changed to --no-dedupe, and may be removed in a future version.
+If you are looking to display all workspace members, use the --workspace flag.
+...
+"#]]).run();
+}