* Add tests for stream continuity during iteration

Author: PardhavMaradani

package/MDAnalysis/coordinates/base.py

@@ -2008,7 +2008,9 @@ def _reopen(self):
             raise RuntimeError(
                 "{}: Cannot reopen stream".format(self.__class__.__name__)
             )
-        self._frame = -1
+        if self._frame == 0:
+            # only reset when stream hasn't been iterated using next
+            self._frame = -1
         self._reopen_called = True
 
     def timeseries(self, **kwargs):

testsuite/MDAnalysisTests/coordinates/test_imd.py

@@ -558,6 +558,27 @@ def test_iterate_current_frame_no_transformations(self, reader):
         p2 = reader[reader.frame].positions
         assert_allclose(p1, p2)
 
+    def test_iterate_continuity_1(self, reader):
+        step = -1
+        for ts in reader:
+            step += 1
+            assert ts.data["step"] == step
+            if step == 4:
+                break
+
+    def test_iterate_continuity_2(self, reader):
+        ts = reader[0]
+        assert ts.data["step"] == 0
+        reader.next()
+        ts = reader[1]
+        assert ts.data["step"] == 1
+        step = 1
+        for ts in reader:
+            step += 1
+            assert ts.data["step"] == step
+            if step == 4:
+                break
+
 
 @pytest.mark.skipif(not HAS_IMDCLIENT, reason="IMDClient not installed")
 class TestAnalysisClasses: