Replace global system test files with local ones and add tests

Instead of using '/etc/hosts' and similar files for testing it is more
portable and 'unit test'-like to use files provided with this repository.

Add tests to verify files specified not as paths (str) but as
py.path.local are accepted as well.

tests/_fixture_files/huckleberry.txt

@@ -0,0 +1,36 @@
+CHAPTER I.
+
+YOU don't know about me without you have read a book by the name of The
+Adventures of Tom Sawyer; but that ain't no matter.  That book was made by
+Mr. Mark Twain, and he told the truth, mainly.  There was things which he
+stretched, but mainly he told the truth.  That is nothing.  I never seen
+anybody but lied one time or another, without it was Aunt Polly, or the
+widow, or maybe Mary.  Aunt Polly—Tom's Aunt Polly, she is—and Mary, and
+the Widow Douglas is all told about in that book, which is mostly a true
+book, with some stretchers, as I said before.
+
+Now the way that the book winds up is this:  Tom and me found the money
+that the robbers hid in the cave, and it made us rich.  We got six
+thousand dollars apiece—all gold.  It was an awful sight of money when it
+was piled up.  Well, Judge Thatcher he took it and put it out at interest,
+and it fetched us a dollar a day apiece all the year round—more than a
+body could tell what to do with.  The Widow Douglas she took me for her
+son, and allowed she would sivilize me; but it was rough living in the
+house all the time, considering how dismal regular and decent the widow
+was in all her ways; and so when I couldn't stand it no longer I lit out.
+I got into my old rags and my sugar-hogshead again, and was free and
+satisfied.  But Tom Sawyer he hunted me up and said he was going to start
+a band of robbers, and I might join if I would go back to the widow and be
+respectable.  So I went back.
+
+The widow she cried over me, and called me a poor lost lamb, and she
+called me a lot of other names, too, but she never meant no harm by it.
+She put me in them new clothes again, and I couldn't do nothing but sweat
+and sweat, and feel all cramped up.  Well, then, the old thing commenced
+again.  The widow rung a bell for supper, and you had to come to time.
+When you got to the table you couldn't go right to eating, but you had to
+wait for the widow to tuck down her head and grumble a little over the
+victuals, though there warn't really anything the matter with them,—that
+is, nothing only everything was cooked by itself.  In a barrel of odds and
+ends it is different; things get mixed up, and the juice kind of swaps
+around, and the things go better.

tests/test_pytest_datafiles.py

@@ -1,23 +1,64 @@
+import os
+import py
 import pytest
 
 
-@pytest.mark.datafiles("/etc/hosts")
-def test_copy_hosts(datafiles):
+TEST_DIR = os.path.dirname(os.path.realpath(__file__))
+FIXTURE_DIR = os.path.join(TEST_DIR, '_fixture_files')
+FIXTURE_FILES = [
+    os.path.join(FIXTURE_DIR, name)
+    for name in [
+        'huckleberry.txt',
+        'random.bin',
+        'sparrow.jpg',
+        ]
+    ]
+
+
+@pytest.mark.datafiles(
+    py.path.local(
+        FIXTURE_FILES[0],  # huckleberry.txt
+	)
+    )
+def test_single_file_pypath(datafiles):
+    """
+    Verify that a single file (py.path.local) is copied correctly
+    """
+    assert (datafiles / 'huckleberry.txt').check(file=1)
+    assert 'Mark Twain' in (datafiles / 'huckleberry.txt').read_text('utf-8')
+
+
+@pytest.mark.datafiles(FIXTURE_FILES[0])  # huckleberry.txt
+def test_single_file_str(datafiles):
+    """
+    Verify that a single file (str) is copied correctly
+    """
+    assert (datafiles / 'huckleberry.txt').check(file=1)
+    assert 'Mark Twain' in (datafiles / 'huckleberry.txt').read_text('utf-8')
+
+
+@pytest.mark.datafiles(
+    *[py.path.local(p) for p in FIXTURE_FILES]
+    )
+def test_multiple_files_pypath(datafiles):
     """
-    Verify that a 'hosts' file containing an entry 'localhost' has been copied
+    Verify multiple files (py.path.local) are copied correctly
     """
-    assert (datafiles / 'hosts').check(file=1)
-    assert 'localhost' in (datafiles / 'hosts').read_text('utf-8')
+    assert (datafiles / 'huckleberry.txt').check(file=1)
+    assert (datafiles / 'random.bin').check(file=1)
+    assert (datafiles / 'sparrow.jpg').check(file=1)
+    assert len((datafiles).listdir()) == 3
 
 
-@pytest.mark.datafiles("/etc/hosts", "/etc/hostname")
-def test_multiple_files(datafiles):
+@pytest.mark.datafiles(*FIXTURE_FILES)
+def test_multiple_files_str(datafiles):
     """
-    Verify multiple files are found
+    Verify multiple files (str) are copied correctly
     """
-    assert (datafiles / 'hosts').check(file=1)
-    assert (datafiles / 'hostname').check(file=1)
-    assert len((datafiles).listdir()) == 2
+    assert (datafiles / 'huckleberry.txt').check(file=1)
+    assert (datafiles / 'random.bin').check(file=1)
+    assert (datafiles / 'sparrow.jpg').check(file=1)
+    assert len((datafiles).listdir()) == 3
 
 
 @pytest.mark.datafiles