add wrapper around field->write_filtered test

TurTLE/test/test_write_filtered.py

+#! /usr/bin/env python
+
+import numpy as np
+import h5py
+import sys
+
+import TurTLE
+from TurTLE import TEST
+
+try:
+    import matplotlib.pyplot as plt
+except:
+    plt = None
+
+def main():
+    c = TEST()
+    c.launch(
+            ['write_filtered_test',
+             '--simname', 'write_filtered_test',
+             '--np', '4',
+             '--ntpp', '1',
+             '--wd', './'] +
+             sys.argv[1:])
+    df = h5py.File('data_for_write_filtered.h5', 'r')
+    bla0 = df['scal_field_full/complex/0'][:, 0]
+    bla1 = df['scal_field_z0slice/complex/0'][...]
+    assert(np.max(np.abs(bla1 - bla0)) < 1e-5)
+    print('SUCCESS!!! z=0 slice agrees between different datasets')
+    return None
+
+if __name__ == '__main__':
+    main()
+