add UT for new features in XYZWriter

package/MDAnalysis/coordinates/XYZ.py

@@ -141,8 +141,15 @@ class XYZWriter(base.WriterBase):
     # these are assumed!
     units = {'time': 'ps', 'length': 'Angstrom'}
 
-    def __init__(self, filename, n_atoms=None, convert_units=True,
-                 remark=None, precision=5, **kwargs):
+    def __init__(
+        self,
+        filename,
+        n_atoms=None,
+        convert_units=True,
+        remark=None,
+        precision=5,
+        **kwargs,
+    ):
         """Initialize the XYZ trajectory writer
 
         Parameters

testsuite/MDAnalysisTests/coordinates/test_xyz.py

@@ -23,6 +23,7 @@
 import pytest
 
 import MDAnalysis as mda
+from MDAnalysis import transformations as trans
 import numpy as np
 from numpy.testing import (
     assert_almost_equal,
@@ -122,6 +123,37 @@ def test_remark(self, universe, remarkout, remarkin, ref, tmpdir):
 
                 assert lines[1].strip() == remarkin
 
+    def test_remark_cellinfo(self, universe, tmpdir):
+        outfile = "write-remark-cellinfo.xyz"
+        universe_cpy = universe.copy()
+        transform = trans.boxdimensions.set_dimensions(
+            [10.0, 10.0, 20.0, 90, 90, 90]
+        )
+        universe_cpy.trajectory.add_transformations(transform)
+        cell = np.array(
+            [[10.0, 0.0, 0.0], [0.0, 10.0, 0.0], [0.0, 0.0, 20.0]]
+        ).flatten()
+        ref_header = (
+            'Lattice="%s" pbc"T T T"'
+            % np.array2string(cell, max_line_width=500)[1:-1]
+        )
+        with tmpdir.as_cwd():
+            universe_cpy.atoms.write(outfile)
+            with open(outfile, "r") as xyzout:
+                lines = xyzout.readlines()
+                assert lines[1].strip() == ref_header
+
+    def test_precision(self, universe, tmpdir):
+        outfile = "write-precision.xyz"
+        precision = 10
+
+        with tmpdir.as_cwd():
+            universe.atoms.write(outfile, precision=precision)
+            with open(outfile, "r") as xyzout:
+                lines = xyzout.readlines()
+                # check that the precision is set correctly
+                assert len(lines[2].split()[1].split(".")[1]) == precision
+
 
 class XYZ_BZ_Reference(XYZReference):
     def __init__(self):