Adding test from readme

tests/test_readme.py

@@ -0,0 +1,20 @@
+from numpythia import Pythia, hepmc_write, hepmc_read
+from numpythia import STATUS, HAS_END_VERTEX, ABS_PDG_ID
+from numpythia.testcmnd import get_cmnd
+from numpy.testing import assert_array_equal
+
+def test_first_example():
+    pythia = Pythia(get_cmnd('w'), random_state=1)
+
+    selection = ((STATUS == 1) & ~HAS_END_VERTEX &
+                (ABS_PDG_ID != 12) & (ABS_PDG_ID != 14) & (ABS_PDG_ID != 16))
+
+    # generate events while writing to ascii hepmc
+    for event in hepmc_write('events.hepmc', pythia(events=1)):
+       array1 = event.all(selection)
+
+    # read the same event back from ascii hepmc
+    for event in hepmc_read('events.hepmc'):
+       array2 = event.all(selection)
+
+    assert_array_equal(array1, array2)