diff --git a/tests/test_vendor.py b/tests/test_vendor.py
index 17c57340..4d7cf196 100644
--- a/tests/test_vendor.py
+++ b/tests/test_vendor.py
@@ -1,5 +1,6 @@
 # Make sure we use the patched packages.
 import pipenv  # noqa
+import os
 
 from prettytoml import lexer
 from prettytoml.elements.atomic import AtomicElement
@@ -7,6 +8,7 @@ from prettytoml.elements.metadata import (
     WhitespaceElement, PunctuationElement, CommentElement
 )
 from prettytoml.elements.table import TableElement
+from pipenv.vendor.pipfile.api import PipfileParser
 
 
 def test_table():
@@ -27,3 +29,36 @@ def test_table():
     assert set(table.items()) == {('id', 42), ('age', 14)}
     del table['id']
     assert set(table.items()) == {('age', 14)}
+
+
+class TestPipfileParser:
+
+    def test_inject_environment_variables(self):
+        os.environ['PYTEST_PIPFILE_TEST'] = "XYZ"
+        p = PipfileParser()
+
+        parsed_dict = p.inject_environment_variables({
+            "a_string": "https://$PYTEST_PIPFILE_TEST@something.com",
+            "another_string": "https://${PYTEST_PIPFILE_TEST}@something.com",
+            "nested": {
+                "a_string": "https://$PYTEST_PIPFILE_TEST@something.com",
+                "another_string": "${PYTEST_PIPFILE_TEST}",
+            },
+            "list": [
+                {
+                    "a_string": "https://$PYTEST_PIPFILE_TEST@something.com",
+                    "another_string": "${PYTEST_PIPFILE_TEST}"
+                },
+                {},
+            ],
+            "bool": True,
+            "none": None,
+        })
+
+        assert parsed_dict["a_string"] == "https://XYZ@something.com"
+        assert parsed_dict["another_string"] == "https://XYZ@something.com"
+        assert parsed_dict["nested"]["another_string"] == "XYZ"
+        assert parsed_dict["list"][0]["a_string"] == "https://XYZ@something.com"
+        assert parsed_dict["list"][1] == {}
+        assert parsed_dict["bool"] is True
+        assert parsed_dict["none"] is None