diff --git a/lib/components/fabro-sandbox/src/test_support.rs b/lib/components/fabro-sandbox/src/test_support.rs
index 67f2d9d09..7b9b8ad96 100644
--- a/lib/components/fabro-sandbox/src/test_support.rs
+++ b/lib/components/fabro-sandbox/src/test_support.rs
@@ -280,10 +280,13 @@ impl MockSandbox {
     }
 
     /// The explicit variables of the last command as the caller passed them.
+    /// The driver's Bash helper records its own `BASH_ENV` blank on the
+    /// spec; that is not the caller's.
     pub fn captured_env_vars(&self) -> Option<HashMap<String, String>> {
         self.recorded().last().map(|spec| {
             spec.env
                 .iter()
+                .filter(|(key, _)| key.as_str() != sandbox_driver::BASH_ENV_VAR)
                 .map(|(k, v)| (k.clone(), v.clone()))
                 .collect()
         })