Add tests and recursion check for link str

pystac/link.py

@@ -203,6 +203,10 @@ def get_target_str(self) -> Optional[str]:
         else:
             return None
 
+    def has_target_href(self) -> bool:
+        """Returns true if this link has a string href in its target information."""
+        return self._target_href is not None
+
     def __repr__(self) -> str:
         return "<Link rel={} target={}>".format(self.rel, self.target)
 

pystac/stac_object.py

@@ -158,7 +158,7 @@ def get_self_href(self) -> Optional[str]:
             links have absolute (as opposed to relative) HREFs.
         """
         self_link = self.get_single_link(pystac.RelType.SELF)
-        if self_link:
+        if self_link and self_link.has_target_href():
             return self_link.get_target_str()
         else:
             return None

tests/test_link.py

@@ -95,6 +95,24 @@ def test_resolved_self_href(self) -> None:
             link.resolve_stac_object()
             self.assertEqual(link.get_absolute_href(), path)
 
+    def test_target_getter_setter(self) -> None:
+        link = pystac.Link("my rel", target="./foo/bar.json")
+        self.assertEqual(link.target, "./foo/bar.json")
+        self.assertEqual(link.get_target_str(), "./foo/bar.json")
+
+        link.target = self.item
+        self.assertEqual(link.target, self.item)
+        self.assertEqual(link.get_target_str(), self.item.get_self_href())
+
+        link.target = "./bar/foo.json"
+        self.assertEqual(link.target, "./bar/foo.json")
+
+    def test_get_target_str_no_href(self) -> None:
+        self.item.remove_links("self")
+        link = pystac.Link("self", target=self.item)
+        self.item.add_link(link)
+        self.assertIsNone(link.get_target_str())
+
 
 class StaticLinkTest(unittest.TestCase):
     def setUp(self) -> None: