Reset branch and added pytest

package/MDAnalysis/coordinates/chain.py

@@ -271,6 +271,13 @@ def __init__(self, filenames, skip=1, dt=None, continuous=False,
                         for filename in filenames]
         self.filenames = np.array([fn[0] if isinstance(fn, tuple) else fn
                                                         for fn in filenames])
+        # Set filenames array to array of "None" if chainreader initialized with
+        # numpy arrays
+        if isinstance(filenames[0], np.ndarray):
+            self.filenames = np.array(["None" for _ in range(len(filenames))])
+        else:
+            self.filenames = np.array([fn[0] if isinstance(fn, tuple) else fn
+                                      for fn in filenames])
         # pointer to "active" trajectory index into self.readers
         self.__active_reader_index = 0
 
@@ -597,7 +604,9 @@ def close(self):
         self._apply('close')
 
     def __repr__(self):
-        if len(self.filenames) > 3:
+        if self.filenames[0] == "None":
+            fnames = "NumPy array"
+        elif len(self.filenames) > 3:
             fnames = "{fname} and {nfanmes} more".format(
                     fname=os.path.basename(self.filenames[0]),
                     nfanmes=len(self.filenames) - 1)

testsuite/MDAnalysisTests/coordinates/test_chainreader.py

@@ -455,3 +455,9 @@ def wrapped(ts):
     # in the issue report values of ~25 were seen before the fix
     # with the fix all values should be <1e-6
     assert np.abs(com).max() < 1e-6
+
+def test_issue_3349():
+    # test for repr of a chainreader when the subreaders are memoryreaders 
+    cdx = np.random.random(3341*3*10).reshape(-1, 3341, 3).astype(np.float32) * 10
+    u = mda.Universe(PSF, (cdx, cdx))
+    assert(repr(u.trajectory) == "<ChainReader containing NumPy array with 20 frames of 3341 atoms>")