Add test cases for the CLI help menu (#4904)

No changes in behavior here, adding these test cases to demonstrate
changes to come.

crates/uv/tests/common/mod.rs

@@ -281,6 +281,13 @@ impl TestContext {
         }
     }
 
+    /// Create a `uv` command for testing.
+    pub fn command(&self) -> Command {
+        let mut command = Command::new(get_bin());
+        self.add_shared_args(&mut command);
+        command
+    }
+
     /// Shared behaviour for almost all test commands.
     ///
     /// * Use a temporary cache directory
@@ -359,6 +366,14 @@ impl TestContext {
         command
     }
 
+    /// Create a `uv help` command with options shared across scenarios.
+    #[allow(clippy::unused_self)]
+    pub fn help(&self) -> Command {
+        let mut command = Command::new(get_bin());
+        command.arg("help");
+        command
+    }
+
     /// Create a `uv sync` command with options shared across scenarios.
     pub fn sync(&self) -> Command {
         let mut command = Command::new(get_bin());