diff --git a/crates/test-support/src/lib.rs b/crates/test-support/src/lib.rs
index aff7398f..04c789bd 100644
--- a/crates/test-support/src/lib.rs
+++ b/crates/test-support/src/lib.rs
@@ -42,6 +42,8 @@ pub fn project() -> Project {
                 [lib]
                 crate-type = ["cdylib"]
 
+                # XXX: It is important that `[dependencies]` is the last section
+                # here, so that `add_local_dependency` functions correctly!
                 [dependencies]
                 wasm-bindgen = {{ path = '{}' }}
             "#, IDX.with(|x| *x), dir.display())),
@@ -142,6 +144,20 @@ impl Project {
         self
     }
 
+    pub fn add_local_dependency(&mut self, name: &str, path: &str) -> &mut Project {
+        {
+            let cargo_toml = self.files
+                .iter_mut()
+                .find(|f| f.0 == "Cargo.toml")
+                .expect("should have Cargo.toml file!");
+            cargo_toml.1.push_str(name);
+            cargo_toml.1.push_str(" = { path = \"");
+            cargo_toml.1.push_str(path);
+            cargo_toml.1.push_str("\" }");
+        }
+        self
+    }
+
     pub fn test(&mut self) {
         let root = root();
         drop(fs::remove_dir_all(&root));