Our approach breaks if test/Project.toml is used

test/ambiguous.jl

@@ -20,6 +20,17 @@ function get_project_dict()
     return project_dict
 end
 
+# If someone makes a PR to this repo to add a
+# `test/Project.toml` file, then this whole approach will break.
+function assert_no_test_project_toml()
+    root_test = @__DIR__ # ./test/
+    root_test_project_toml = joinpath(root_test, "Project.toml") # ./test/Project.toml
+    if ispath(root_test_project_toml)
+        error("Currently, we don't support test/Project.toml in this repo")
+    end
+    return nothing
+end
+
 function get_test_deps()
     project_dict = get_project_dict()
     targets_section = project_dict["targets"]
@@ -50,6 +61,7 @@ end
 # via `Pkg.test`. Therefore, test deps must be manually
 # installed if missing.
 function install_all_test_deps()
+    assert_no_test_project_toml()
     test_deps = get_test_deps()
 
     # If all the test deps are already available,