diff --git a/qutebrowser/misc/lineparser.py b/qutebrowser/misc/lineparser.py
index b9300a392..4999c2e22 100644
--- a/qutebrowser/misc/lineparser.py
+++ b/qutebrowser/misc/lineparser.py
@@ -92,6 +92,12 @@ class BaseLineParser(QObject):
 
         Args:
             mode: The mode to use ('a'/'r'/'w')
+
+        Raises:
+            IOError: if the file is already open
+
+        Yields:
+            a file object for the config file
         """
         assert self._configfile is not None
         if self._opened:
diff --git a/tests/unit/misc/test_lineparser.py b/tests/unit/misc/test_lineparser.py
index 7cf7a73b7..a37a5fe27 100644
--- a/tests/unit/misc/test_lineparser.py
+++ b/tests/unit/misc/test_lineparser.py
@@ -21,6 +21,7 @@
 
 import os
 import pytest
+from unittest import mock
 
 from qutebrowser.misc import lineparser as lineparsermod
 
@@ -53,9 +54,49 @@ class TestBaseLineParser:
         lineparser._prepare_save()
         os_mock.makedirs.assert_called_with(self.CONFDIR, 0o755)
 
+    def test_prepare_save_no_config(self, mocker):
+        """Test if _prepare_save doesn't create a None config dir."""
+        os_mock = mocker.patch('qutebrowser.misc.lineparser.os')
+        os_mock.path.exists.return_value = True
+
+        lineparser = lineparsermod.BaseLineParser(None, self.FILENAME)
+        assert not lineparser._prepare_save()
+        assert not os_mock.makedirs.called
+
+    def test_double_open(self, mocker, lineparser):
+        """Test if _open refuses reentry."""
+        mocker.patch('qutebrowser.misc.lineparser.open', mock.mock_open())
+
+        with lineparser._open('r'):
+            with pytest.raises(IOError):
+                with lineparser._open('r'):
+                    pass
+
+    def test_binary(self, mocker):
+        """Test if _open and _write correctly handle binary files."""
+        open_mock = mock.mock_open()
+        mocker.patch('qutebrowser.misc.lineparser.open', open_mock)
+
+        testdata = b'\xf0\xff'
+
+        lineparser = lineparsermod.BaseLineParser(
+            self.CONFDIR, self.FILENAME, binary=True)
+        with lineparser._open('r') as f:
+            lineparser._write(f, [testdata])
+
+        open_mock.assert_called_once_with(
+            os.path.join(self.CONFDIR, self.FILENAME), 'rb')
+
+        open_mock().write.assert_has_calls([
+            mock.call(testdata),
+            mock.call(b'\n')
+        ])
+
 
 class TestLineParser:
 
+    """Tests for LineParser."""
+
     @pytest.fixture
     def lineparser(self, tmpdir):
         """Fixture to get a LineParser for tests."""
@@ -63,7 +104,18 @@ class TestLineParser:
         lp.save()
         return lp
 
+    def test_init(self, tmpdir):
+        """Test if creating a line parser correctly reads its file."""
+        (tmpdir / 'file').write('one\ntwo\n')
+        lineparser = lineparsermod.LineParser(str(tmpdir), 'file')
+        assert lineparser.data == ['one', 'two']
+
+        (tmpdir / 'file').write_binary(b'\xfe\n\xff\n')
+        lineparser = lineparsermod.LineParser(str(tmpdir), 'file', binary=True)
+        assert lineparser.data == [b'\xfe', b'\xff']
+
     def test_clear(self, tmpdir, lineparser):
+        """Test if clear() empties its file."""
         lineparser.data = ['one', 'two']
         lineparser.save()
         assert (tmpdir / 'file').read() == 'one\ntwo\n'
@@ -71,6 +123,20 @@ class TestLineParser:
         assert not lineparser.data
         assert (tmpdir / 'file').read() == ''
 
+    def test_double_open(self, lineparser):
+        """Test if save() bails on an already open file."""
+        with lineparser._open('r'):
+            with pytest.raises(IOError):
+                lineparser.save()
+
+    def test_prepare_save(self, tmpdir, lineparser):
+        """Test if save() bails when _prepare_save() returns False."""
+        (tmpdir / 'file').write('pristine\n')
+        lineparser.data = ['changed']
+        lineparser._prepare_save = lambda: False
+        lineparser.save()
+        assert (tmpdir / 'file').read() == 'pristine\n'
+
 
 class TestAppendLineParser:
 
@@ -97,7 +163,17 @@ class TestAppendLineParser:
         lineparser.save()
         assert (tmpdir / 'file').read() == self._get_expected(new_data)
 
+    def test_save_without_configdir(self, tmpdir, lineparser):
+        """Test save() failing because no configdir was set."""
+        new_data = ['new data 1', 'new data 2']
+        lineparser.new_data = new_data
+        lineparser._configdir = None
+        assert not lineparser.save()
+        # make sure new data is still there
+        assert lineparser.new_data == new_data
+
     def test_clear(self, tmpdir, lineparser):
+        """Check if calling clear() empties both pending and persisted data."""
         lineparser.new_data = ['one', 'two']
         lineparser.save()
         assert (tmpdir / 'file').read() == "old data 1\nold data 2\none\ntwo\n"
@@ -108,6 +184,14 @@ class TestAppendLineParser:
         assert not lineparser.new_data
         assert (tmpdir / 'file').read() == ""
 
+    def test_clear_without_configdir(self, tmpdir, lineparser):
+        """Test clear() failing because no configdir was set."""
+        new_data = ['new data 1', 'new data 2']
+        lineparser.new_data = new_data
+        lineparser._configdir = None
+        assert not lineparser.clear()
+        assert lineparser.new_data == new_data
+
     def test_iter_without_open(self, lineparser):
         """Test __iter__ without having called open()."""
         with pytest.raises(ValueError):