diff --git a/qutebrowser/completion/completer.py b/qutebrowser/completion/completer.py
index 12f607b51..ebdb1d10b 100644
--- a/qutebrowser/completion/completer.py
+++ b/qutebrowser/completion/completer.py
@@ -22,7 +22,7 @@
 from PyQt5.QtCore import pyqtSignal, pyqtSlot, QObject, QTimer
 
 from qutebrowser.config import config
-from qutebrowser.commands import cmdexc, cmdutils, runners
+from qutebrowser.commands import cmdutils, runners
 from qutebrowser.utils import usertypes, log, objreg, utils
 from qutebrowser.completion.models import instances, sortfilter
 
@@ -485,16 +485,3 @@ class Completer(QObject):
         """Select the next completion item."""
         self._open_completion_if_needed()
         self.next_prev_item.emit(False)
-
-    @cmdutils.register(instance='completion', hide=True,
-                       modes=[usertypes.KeyMode.command], scope='window')
-    def completion_item_del(self):
-        """Delete the current completion item."""
-        completion = objreg.get('completion', scope='window',
-                                window=self._win_id)
-        if not completion.currentIndex().isValid():
-            raise cmdexc.CommandError("No item selected!")
-        try:
-            self.model().srcmodel.delete_cur_item(completion)
-        except NotImplementedError:
-            raise cmdexc.CommandError("Cannot delete this item.")
diff --git a/qutebrowser/completion/completionwidget.py b/qutebrowser/completion/completionwidget.py
index 8c2b8c1fd..80e87dbe4 100644
--- a/qutebrowser/completion/completionwidget.py
+++ b/qutebrowser/completion/completionwidget.py
@@ -29,7 +29,8 @@ from PyQt5.QtCore import pyqtSlot, pyqtSignal, Qt, QItemSelectionModel
 from qutebrowser.config import config, style
 from qutebrowser.completion import completiondelegate, completer
 from qutebrowser.completion.models import base
-from qutebrowser.utils import qtutils, objreg, utils
+from qutebrowser.utils import qtutils, objreg, utils, usertypes
+from qutebrowser.commands import cmdexc, cmdutils
 
 
 class CompletionView(QTreeView):
@@ -277,3 +278,14 @@ class CompletionView(QTreeView):
         if scrollbar is not None:
             scrollbar.setValue(scrollbar.minimum())
         super().showEvent(e)
+
+    @cmdutils.register(instance='completion', hide=True,
+                       modes=[usertypes.KeyMode.command], scope='window')
+    def completion_item_del(self):
+        """Delete the current completion item."""
+        if not self.currentIndex().isValid():
+            raise cmdexc.CommandError("No item selected!")
+        try:
+            self.model().srcmodel.delete_cur_item(self)
+        except NotImplementedError:
+            raise cmdexc.CommandError("Cannot delete this item.")
diff --git a/tests/helpers/fixtures.py b/tests/helpers/fixtures.py
index 2530a1ab6..eb8dd9a97 100644
--- a/tests/helpers/fixtures.py
+++ b/tests/helpers/fixtures.py
@@ -255,6 +255,14 @@ def app_stub(stubs):
     objreg.delete('app')
 
 
+@pytest.yield_fixture
+def completion_widget_stub(win_registry):
+    stub = unittest.mock.Mock()
+    objreg.register('completion', stub, scope='window', window=0)
+    yield stub
+    objreg.delete('completion', scope='window', window=0)
+
+
 @pytest.fixture(scope='session')
 def stubs():
     """Provide access to stub objects useful for testing."""
diff --git a/tests/helpers/stubs.py b/tests/helpers/stubs.py
index fa7f60fa5..d08b35f60 100644
--- a/tests/helpers/stubs.py
+++ b/tests/helpers/stubs.py
@@ -27,7 +27,7 @@ from unittest import mock
 from PyQt5.QtCore import pyqtSignal, QPoint, QProcess, QObject
 from PyQt5.QtNetwork import (QNetworkRequest, QAbstractNetworkCache,
                              QNetworkCacheMetaData)
-from PyQt5.QtWidgets import QCommonStyle, QWidget
+from PyQt5.QtWidgets import QCommonStyle, QWidget, QLineEdit
 
 from qutebrowser.browser.webkit import webview, history
 from qutebrowser.config import configexc
@@ -293,12 +293,13 @@ class FakeCommand:
     """A simple command stub which has a description."""
 
     def __init__(self, name='', desc='', hide=False, debug=False,
-                 deprecated=False):
+                 deprecated=False, completion=None):
         self.desc = desc
         self.name = name
         self.hide = hide
         self.debug = debug
         self.deprecated = deprecated
+        self.completion = completion
 
 
 class FakeTimer(QObject):
@@ -359,6 +360,24 @@ class FakeConfigType:
         self.complete = lambda: [(val, '') for val in valid_values]
 
 
+class FakeStatusbarCommand(QLineEdit):
+
+    """Stub for the statusbar command prompt."""
+
+    got_cmd = pyqtSignal(str)
+    clear_completion_selection = pyqtSignal()
+    hide_completion = pyqtSignal()
+    update_completion = pyqtSignal()
+    show_cmd = pyqtSignal()
+    hide_cmd = pyqtSignal()
+
+    def __init__(self, parent=None):
+        super().__init__(parent)
+
+    def prefix(self):
+        return self.text()[0]
+
+
 class ConfigStub(QObject):
 
     """Stub for the config module.
diff --git a/tests/unit/completion/test_completer.py b/tests/unit/completion/test_completer.py
new file mode 100644
index 000000000..bfb1f0718
--- /dev/null
+++ b/tests/unit/completion/test_completer.py
@@ -0,0 +1,223 @@
+# vim: ft=python fileencoding=utf-8 sts=4 sw=4 et:
+
+# Copyright 2016 Ryan Roden-Corrent (rcorre) <ryan@rcorre.net>
+#
+# This file is part of qutebrowser.
+#
+# qutebrowser is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# qutebrowser is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with qutebrowser.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Tests for the Completer Object."""
+
+import unittest.mock
+
+import pytest
+from PyQt5.QtGui import QStandardItemModel
+
+from qutebrowser.completion import completer
+from qutebrowser.utils import usertypes
+
+
+class FakeCompletionModel(QStandardItemModel):
+
+    """Stub for a completion model."""
+
+    DUMB_SORT = None
+
+    def __init__(self, kind, parent=None):
+        super().__init__(parent)
+        self.kind = kind
+
+
+@pytest.fixture
+def cmd(stubs, qtbot):
+    """Create the statusbar command prompt the completer uses."""
+    cmd = stubs.FakeStatusbarCommand()
+    qtbot.addWidget(cmd)
+    return cmd
+
+
+@pytest.fixture
+def completer_obj(qtbot, cmd, config_stub):
+    """Create the completer used for testing."""
+    config_stub.data = {'completion': {'auto-open': False}}
+    return completer.Completer(cmd, 0)
+
+
+@pytest.fixture(autouse=True)
+def instances(monkeypatch):
+    """Mock the instances module so get returns a fake completion model."""
+    # populate a model for each completion type, with a nested structure for
+    # option and value completion
+    instances = {kind: FakeCompletionModel(kind)
+                 for kind in usertypes.Completion}
+    instances[usertypes.Completion.option] = {
+        'general': FakeCompletionModel(usertypes.Completion.option),
+    }
+    instances[usertypes.Completion.value] = {
+        'general': {
+            'ignore-case': FakeCompletionModel(usertypes.Completion.value),
+        }
+    }
+    monkeypatch.setattr('qutebrowser.completion.completer.instances',
+                        instances)
+
+
+@pytest.fixture(autouse=True)
+def cmdutils_patch(monkeypatch, stubs):
+    """Patch the cmdutils module to provide fake commands."""
+    cmds = {
+        'set': [usertypes.Completion.section, usertypes.Completion.option,
+                usertypes.Completion.value],
+        'help': [usertypes.Completion.helptopic],
+        'quickmark-load': [usertypes.Completion.quickmark_by_name],
+        'bookmark-load': [usertypes.Completion.bookmark_by_url],
+        'open': [usertypes.Completion.url],
+        'buffer': [usertypes.Completion.tab],
+        'session-load': [usertypes.Completion.sessions],
+        'bind': [usertypes.Completion.empty, usertypes.Completion.command],
+        'tab-detach': None,
+    }
+    cmd_utils = stubs.FakeCmdUtils({
+        name: stubs.FakeCommand(completion=compl)
+        for name, compl in cmds.items()
+    })
+    monkeypatch.setattr('qutebrowser.completion.completer.cmdutils',
+                        cmd_utils)
+
+
+def _set_cmd_prompt(cmd, txt):
+    """Set the command prompt's text and cursor position.
+
+    Args:
+        cmd: The command prompt object.
+        txt: The prompt text, using | as a placeholder for the cursor position.
+    """
+    cmd.setText(txt.replace('|', ''))
+    cmd.setCursorPosition(txt.index('|'))
+
+
+def _validate_cmd_prompt(cmd, txt):
+    """Interpret fake command prompt text using | as the cursor placeholder.
+
+    Args:
+        cmd: The command prompt object.
+        txt: The prompt text, using | as a placeholder for the cursor position.
+    """
+    assert cmd.cursorPosition() == txt.index('|')
+    assert cmd.text() == txt.replace('|', '')
+
+
+@pytest.mark.parametrize('txt, expected', [
+    (':nope|', usertypes.Completion.command),
+    (':nope |', None),
+    (':set |', usertypes.Completion.section),
+    (':set gen|', usertypes.Completion.section),
+    (':set general |', usertypes.Completion.option),
+    (':set what |', None),
+    (':set general ignore-case |', usertypes.Completion.value),
+    (':set general huh |', None),
+    (':help |', usertypes.Completion.helptopic),
+    (':quickmark-load |', usertypes.Completion.quickmark_by_name),
+    (':bookmark-load |', usertypes.Completion.bookmark_by_url),
+    (':open |', usertypes.Completion.url),
+    (':buffer |', usertypes.Completion.tab),
+    (':session-load |', usertypes.Completion.sessions),
+    (':bind |', usertypes.Completion.empty),
+    (':bind <c-x> |', usertypes.Completion.command),
+    (':bind <c-x> foo|', usertypes.Completion.command),
+    (':bind <c-x>| foo', usertypes.Completion.empty),
+    (':set| general ', usertypes.Completion.command),
+    (':|set general ', usertypes.Completion.command),
+    (':set gene|ral ignore-case', usertypes.Completion.section),
+    (':|', usertypes.Completion.command),
+    (':   |', usertypes.Completion.command),
+    (':bookmark-load      |', usertypes.Completion.bookmark_by_url),
+    ('/|', None),
+    (':open -t|', None),
+    (':open --tab|', None),
+    (':open -t |', usertypes.Completion.url),
+    (':open --tab |', usertypes.Completion.url),
+    (':open | -t', usertypes.Completion.url),
+    (':--foo --bar |', None),
+    (':tab-detach |', None),
+    (':bind --mode=caret <c-x> |', usertypes.Completion.command),
+    pytest.mark.xfail(reason='issue #74')((':bind --mode caret <c-x> |',
+                                           usertypes.Completion.command)),
+    (':set -t -p |', usertypes.Completion.section),
+    (':open -- |', None),
+])
+def test_update_completion(txt, expected, cmd, completer_obj,
+                           completion_widget_stub):
+    """Test setting the completion widget's model based on command text."""
+    # this test uses | as a placeholder for the current cursor position
+    _set_cmd_prompt(cmd, txt)
+    completer_obj.update_completion()
+    if expected is None:
+        assert not completion_widget_stub.set_model.called
+    else:
+        assert completion_widget_stub.set_model.call_count == 1
+        arg = completion_widget_stub.set_model.call_args[0][0]
+        # the outer model is just for sorting; srcmodel is the completion model
+        assert arg.srcmodel.kind == expected
+
+
+def test_completion_item_prev(completer_obj, cmd, completion_widget_stub,
+                              config_stub, qtbot):
+    """Test that completion_item_prev emits next_prev_item."""
+    cmd.setText(':')
+    with qtbot.waitSignal(completer_obj.next_prev_item) as blocker:
+        completer_obj.completion_item_prev()
+    assert blocker.args == [True]
+
+
+def test_completion_item_next(completer_obj, cmd, completion_widget_stub,
+                              config_stub, qtbot):
+    """Test that completion_item_next emits next_prev_item."""
+    cmd.setText(':')
+    with qtbot.waitSignal(completer_obj.next_prev_item) as blocker:
+        completer_obj.completion_item_next()
+    assert blocker.args == [False]
+
+
+@pytest.mark.parametrize('before, newtxt, quick_complete, count, after', [
+    (':foo |', 'bar', False, 1, ':foo bar|'),
+    (':foo |', 'bar', True, 2, ':foo bar|'),
+    (':foo |', 'bar', True, 1, ':foo bar |'),
+    (':foo | bar', 'baz', False, 1, ':foo baz| bar'),
+    (':foo |', 'bar baz', True, 1, ":foo 'bar baz' |"),
+    (':foo |', '', True, 1, ":foo '' |"),
+    (':foo |', None, True, 1, ":foo |"),
+])
+def test_selection_changed(before, newtxt, count, quick_complete, after,
+                           completer_obj, cmd, completion_widget_stub,
+                           config_stub):
+    """Test that change_completed_part modifies the cmd text properly.
+
+    The | represents the current cursor position in the cmd prompt.
+    If quick-complete is True and there is only 1 completion (count == 1),
+    then we expect a space to be appended after the current word.
+    """
+    config_stub.data['completion']['quick-complete'] = quick_complete
+    model = unittest.mock.Mock()
+    model.data = unittest.mock.Mock(return_value=newtxt)
+    model.count = unittest.mock.Mock(return_value=count)
+    indexes = [unittest.mock.Mock()]
+    selection = unittest.mock.Mock()
+    selection.indexes = unittest.mock.Mock(return_value=indexes)
+    completion_widget_stub.model = unittest.mock.Mock(return_value=model)
+    _set_cmd_prompt(cmd, before)
+    completer_obj.update_cursor_part()
+    completer_obj.selection_changed(selection, None)
+    model.data.assert_called_with(indexes[0])
+    _validate_cmd_prompt(cmd, after)