diff --git a/news/5821.trivial b/news/5821.trivial
new file mode 100644
index 00000000000..25c6284e8b0
--- /dev/null
+++ b/news/5821.trivial
@@ -0,0 +1 @@
+Add unit tests for egg_info_matches.
diff --git a/tests/unit/test_index.py b/tests/unit/test_index.py
index d67aa4d0dd9..bca09a24e4b 100644
--- a/tests/unit/test_index.py
+++ b/tests/unit/test_index.py
@@ -4,7 +4,9 @@
 from pip._vendor import html5lib
 
 from pip._internal.download import PipSession
-from pip._internal.index import Link, PackageFinder, _determine_base_url
+from pip._internal.index import (
+    Link, PackageFinder, _determine_base_url, egg_info_matches,
+)
 
 
 def test_sort_locations_file_expand_dir(data):
@@ -158,3 +160,33 @@ def test_get_formatted_locations_basic_auth():
 
     result = finder.get_formatted_locations()
     assert 'user' not in result and 'pass' not in result
+
+
+@pytest.mark.parametrize(
+    ("egg_info", "search_name", "expected"),
+    [
+        # Trivial.
+        ("pip-18.0", "pip", "18.0"),
+        ("pip-18.0", None, "18.0"),
+
+        # Non-canonical names.
+        ("Jinja2-2.10", "jinja2", "2.10"),
+        ("jinja2-2.10", "Jinja2", "2.10"),
+
+        # Ambiguous names. Should be smart enough if the package name is
+        # provided, otherwise make a guess.
+        ("foo-2-2", "foo", "2-2"),
+        ("foo-2-2", "foo-2", "2"),
+        ("foo-2-2", None, "2-2"),
+        ("im-valid", None, "valid"),
+
+        # Invalid names.
+        ("invalid", None, None),
+        ("im_invalid", None, None),
+        ("the-package-name-8.19", "does-not-match", None),
+    ],
+)
+def test_egg_info_matches(egg_info, search_name, expected):
+    link = None     # Only used for reporting.
+    version = egg_info_matches(egg_info, search_name, link)
+    assert version == expected