Add tests

Author: Andy-Python-Programmer

src/cargo/util/config/mod.rs

@@ -450,16 +450,20 @@ impl Config {
         if let Some(dir) = &self.target_dir {
             Ok(Some(dir.clone()))
         } else if let Some(dir) = env::var_os("CARGO_TARGET_DIR") {
+            // Check if the CARGO_TARGET_DIR environment variable is set to an empty string.
             if dir.to_string_lossy() == "" {
-                anyhow::bail!("the target directory is set to an empty string")
+                anyhow::bail!("the target directory is set to an empty string in the CARGO_TARGET_DIR environment variable.")
             }
 
             Ok(Some(Filesystem::new(self.cwd.join(dir))))
         } else if let Some(val) = &self.build_config()?.target_dir {
             let path = val.resolve_path(self);
 
+            // Check if the target directory is set to an empty string in the config.toml file.
             if val.raw_value() == "" {
-                anyhow::bail!("the target directory is set to an empty string")
+                anyhow::bail!(
+                    "the target directory is set to an empty string in the config.toml file.",
+                )
             }
 
             Ok(Some(Filesystem::new(path)))

tests/testsuite/config.rs

@@ -1497,6 +1497,17 @@ target-dir = ''
 
     assert_error(
         config.target_dir().unwrap_err(),
-        "the target directory is set to an empty string",
+        "the target directory is set to an empty string in the config.toml file.",
     );
 }
+
+#[cargo_test]
+fn cargo_target_empty_env() {
+    let project = project().build();
+
+    project.cargo("build")
+        .env("CARGO_TARGET_DIR", "")
+        .with_stderr("error: the target directory is set to an empty string in the CARGO_TARGET_DIR environment variable.")
+        .with_status(101)
+        .run()
+}