Add context options: -A/-B/-C; Fixes #287 (#722)

* Add context options: -A/-B/-C; Fixes #287

* Fix indentation of line continuation.

* Fix 'only before context' case.

* Add some tests for the new context options.

* Refactor context code (pass context tuple, instead of before/after variables)

* Get rid of 'remove temp file code' in context test.

* Fix reintroduced error (regarding 'only before context').

codespell_lib/tests/test_basic.py

@@ -302,6 +302,65 @@ def test_case_handling(tmpdir, capsys):
         os.remove(f.name)
 
 
+def test_context(tmpdir, capsys):
+    """Test context options."""
+    d = str(tmpdir)
+    with open(op.join(d, 'context.txt'), 'w') as f:
+        f.write('line 1\nline 2\nline 3 abandonned\nline 4\nline 5')
+
+    # symmetric context, fully within file
+    cs.main('-C', '1', d)
+    lines = capsys.readouterr()[0].split('\n')
+    assert len(lines) == 5
+    assert lines[0] == ': line 2'
+    assert lines[1] == '> line 3 abandonned'
+    assert lines[2] == ': line 4'
+
+    # requested context is bigger than the file
+    cs.main('-C', '10', d)
+    lines = capsys.readouterr()[0].split('\n')
+    assert len(lines) == 7
+    assert lines[0] == ': line 1'
+    assert lines[1] == ': line 2'
+    assert lines[2] == '> line 3 abandonned'
+    assert lines[3] == ': line 4'
+    assert lines[4] == ': line 5'
+
+    # only before context
+    cs.main('-B', '2', d)
+    lines = capsys.readouterr()[0].split('\n')
+    assert len(lines) == 5
+    assert lines[0] == ': line 1'
+    assert lines[1] == ': line 2'
+    assert lines[2] == '> line 3 abandonned'
+
+    # only after context
+    cs.main('-A', '1', d)
+    lines = capsys.readouterr()[0].split('\n')
+    assert len(lines) == 4
+    assert lines[0] == '> line 3 abandonned'
+    assert lines[1] == ': line 4'
+
+    # asymmetric context
+    cs.main('-B', '2', '-A', '1', d)
+    lines = capsys.readouterr()[0].split('\n')
+    assert len(lines) == 6
+    assert lines[0] == ': line 1'
+    assert lines[1] == ': line 2'
+    assert lines[2] == '> line 3 abandonned'
+    assert lines[3] == ': line 4'
+
+    # both '-C' and '-A' on the command line
+    cs.main('-C', '2', '-A', '1', d)
+    lines = capsys.readouterr()[0].split('\n')
+    assert 'ERROR' in lines[0]
+
+    # both '-C' and '-B' on the command line
+    cs.main('-C', '2', '-B', '1', d)
+    lines = capsys.readouterr()[0].split('\n')
+    assert 'ERROR' in lines[0]
+
+
 @contextlib.contextmanager
 def FakeStdin(text):
     if sys.version[0] == '2':