diff --git a/skimage/viewer/canvastools/base.py b/skimage/viewer/canvastools/base.py
index 6fcda9c4..7f61ce2c 100644
--- a/skimage/viewer/canvastools/base.py
+++ b/skimage/viewer/canvastools/base.py
@@ -115,7 +115,7 @@ class CanvasToolBase(object):
     @property
     def geometry(self):
         """Geometry information that gets passed to callback functions."""
-        raise NotImplementedError
+        return None
 
 
 class ToolHandles(object):
diff --git a/skimage/viewer/canvastools/linetool.py b/skimage/viewer/canvastools/linetool.py
index c32d0ea7..fed18383 100644
--- a/skimage/viewer/canvastools/linetool.py
+++ b/skimage/viewer/canvastools/linetool.py
@@ -69,7 +69,7 @@ class LineTool(CanvasToolBase):
 
     @property
     def end_points(self):
-        return self._end_pts
+        return self._end_pts.astype(int)
 
     @end_points.setter
     def end_points(self, pts):
@@ -191,7 +191,7 @@ class ThickLineTool(LineTool):
             self.callback_on_change(self.geometry)
 
 
-if __name__ == '__main__':
+if __name__ == '__main__':  # pragma: no cover
     import matplotlib.pyplot as plt
     from skimage import data
 
diff --git a/skimage/viewer/canvastools/painttool.py b/skimage/viewer/canvastools/painttool.py
index 66cec08d..6af8b5d3 100644
--- a/skimage/viewer/canvastools/painttool.py
+++ b/skimage/viewer/canvastools/painttool.py
@@ -198,7 +198,7 @@ class CenteredWindow(object):
         return [slice(ymin, ymax), slice(xmin, xmax)]
 
 
-if __name__ == '__main__':
+if __name__ == '__main__':  # pragma: no cover
     np.testing.rundocs()
     from skimage import data
 
diff --git a/skimage/viewer/canvastools/recttool.py b/skimage/viewer/canvastools/recttool.py
index d4ae113e..f055e439 100644
--- a/skimage/viewer/canvastools/recttool.py
+++ b/skimage/viewer/canvastools/recttool.py
@@ -201,7 +201,7 @@ class RectangleTool(CanvasToolBase, RectangleSelector):
         return self.extents
 
 
-if __name__ == '__main__':
+if __name__ == '__main__':  # pragma: no cover
     import matplotlib.pyplot as plt
     from skimage import data
 
diff --git a/skimage/viewer/plugins/base.py b/skimage/viewer/plugins/base.py
index baded1cb..6b162fd8 100644
--- a/skimage/viewer/plugins/base.py
+++ b/skimage/viewer/plugins/base.py
@@ -239,7 +239,8 @@ class Plugin(QtGui.QDialog):
 
     def clean_up(self):
         self.remove_image_artists()
-        self.image_viewer.plugins.remove(self)
+        if self in self.image_viewer.plugins:
+            self.image_viewer.plugins.remove(self)
         self.image_viewer.reset_image()
         self.image_viewer.redraw()
 
diff --git a/skimage/viewer/plugins/lineprofile.py b/skimage/viewer/plugins/lineprofile.py
index d0011c75..6e5b2c1f 100644
--- a/skimage/viewer/plugins/lineprofile.py
+++ b/skimage/viewer/plugins/lineprofile.py
@@ -46,7 +46,7 @@ class LineProfile(PlotPlugin):
         if self._limit_type == 'image':
             self.limits = (np.min(image), np.max(image))
         elif self._limit_type == 'dtype':
-            self._limit_type = dtype_range[image.dtype.type]
+            self.limits = dtype_range[image.dtype.type]
         elif self._limit_type is None or len(self._limit_type) == 2:
             self.limits = self._limit_type
         else:
@@ -91,6 +91,7 @@ class LineProfile(PlotPlugin):
         profile: list of 1d arrays
             Profile of intensity values. Length 1 (grayscale) or 3 (rgb).
         """
+        self._update_data()
         profiles = [data.get_ydata() for data in self.profile]
         return self.line_tool.end_points, profiles
 
@@ -103,8 +104,15 @@ class LineProfile(PlotPlugin):
     def line_changed(self, end_points):
         x, y = np.transpose(end_points)
         self.line_tool.end_points = end_points
-        scan = measure.profile_line(self.image_viewer.original_image,
-                                    *end_points[:, ::-1],
+        self._update_data()
+        self.ax.relim()
+
+        self._autoscale_view()
+        self.redraw()
+
+    def _update_data(self):
+        scan = measure.profile_line(self.image_viewer.image,
+                                    *self.line_tool.end_points[:, ::-1],
                                     linewidth=self.line_tool.linewidth)
         self.scan_data = scan
         if scan.ndim == 1:
@@ -117,11 +125,6 @@ class LineProfile(PlotPlugin):
             self.profile[i].set_xdata(np.arange(scan.shape[0]))
             self.profile[i].set_ydata(scan[:, i])
 
-        self.ax.relim()
-
-        self._autoscale_view()
-        self.redraw()
-
     def reset_axes(self, scan_data):
         # Clear lines out
         for line in self.ax.lines:
@@ -147,7 +150,7 @@ class LineProfile(PlotPlugin):
             The line scan values across the image.
         """
         end_points = self.line_tool.end_points
-        line_image = np.zeros(self.image_viewer.original_image.shape[:2],
+        line_image = np.zeros(self.image_viewer.image.shape[:2],
                               np.uint8)
         width = self.line_tool.linewidth
         if width > 1:
@@ -162,4 +165,3 @@ class LineProfile(PlotPlugin):
         rr, cc = draw.line(y1, x1, y2, x2)
         line_image[rr, cc] = 255
         return line_image, self.scan_data
-
diff --git a/skimage/viewer/tests/test_plugins.py b/skimage/viewer/tests/test_plugins.py
new file mode 100644
index 00000000..7ef62730
--- /dev/null
+++ b/skimage/viewer/tests/test_plugins.py
@@ -0,0 +1,185 @@
+# -*- coding: utf-8 -*-
+import numpy as np
+import skimage
+import skimage.data as data
+from skimage.filter.rank import median
+from skimage.morphology import disk
+from numpy.testing import assert_equal, assert_allclose, assert_almost_equal
+from numpy.testing.decorators import skipif
+
+try:
+    from skimage.viewer.qt import qt_api
+    from skimage.viewer import ImageViewer
+    from skimage.viewer.plugins import (
+        LineProfile, Measure, CannyPlugin, LabelPainter, Crop, ColorHistogram,
+        PlotPlugin)
+    from skimage.viewer.plugins.base import Plugin
+    from skimage.viewer.widgets import Slider
+    viewer_available = not qt_api is None
+except ImportError:
+    viewer_available = False
+
+
+def setup_line_profile(image, limits='image'):
+    viewer = ImageViewer(skimage.img_as_float(image))
+    plugin = LineProfile(limits=limits)
+    viewer += plugin
+    return plugin
+
+
+@skipif(not viewer_available)
+def test_line_profile():
+    """ Test a line profile using an ndim=2 image"""
+    plugin = setup_line_profile(data.camera())
+    line_image, scan_data = plugin.output()
+    for inp in [line_image.nonzero()[0].size,
+                line_image.sum() / line_image.max(),
+                scan_data.size]:
+        assert_equal(inp, 172)
+    assert_equal(line_image.shape, (512, 512))
+    assert_allclose(scan_data.max(), 0.9176, rtol=1e-3)
+    assert_allclose(scan_data.mean(), 0.2812, rtol=1e-3)
+
+
+@skipif(not viewer_available)
+def test_line_profile_rgb():
+    """ Test a line profile using an ndim=3 image"""
+    plugin = setup_line_profile(data.chelsea(), limits=None)
+    for i in range(6):
+        plugin.line_tool._thicken_scan_line()
+    line_image, scan_data = plugin.output()
+    assert_equal(line_image[line_image == 128].size, 750)
+    assert_equal(line_image[line_image == 255].size, 151)
+    assert_equal(line_image.shape, (300, 451))
+    assert_equal(scan_data.shape, (151, 3))
+    assert_allclose(scan_data.max(), 0.772, rtol=1e-3)
+    assert_allclose(scan_data.mean(), 0.4359, rtol=1e-3)
+
+
+@skipif(not viewer_available)
+def test_line_profile_dynamic():
+    """Test a line profile updating after an image transform"""
+    image = data.coins()[:-50, :]  # shave some off to make the line lower
+    image = skimage.img_as_float(image)
+    viewer = ImageViewer(image)
+
+    lp = LineProfile(limits='dtype')
+    viewer += lp
+
+    line = lp.get_profiles()[-1][0]
+    assert line.size == 129
+    assert_almost_equal(np.std(viewer.image), 0.208, 3)
+    assert_almost_equal(np.std(line), 0.229, 3)
+    assert_almost_equal(np.max(line) - np.min(line), 0.725, 1)
+
+    viewer.image = skimage.img_as_float(median(image,
+                                               selem=disk(radius=3)))
+
+    line = lp.get_profiles()[-1][0]
+    assert_almost_equal(np.std(viewer.image), 0.198, 3)
+    assert_almost_equal(np.std(line), 0.220, 3)
+    assert_almost_equal(np.max(line) - np.min(line), 0.639, 1)
+
+
+@skipif(not viewer_available)
+def test_measure():
+    image = data.camera()
+    viewer = ImageViewer(image)
+    m = Measure()
+    viewer += m
+
+    m.line_changed([(0, 0), (10, 10)])
+    assert_equal(str(m._length.text), '14.1')
+    assert_equal(str(m._angle.text[:5]), '135.0')
+
+
+@skipif(not viewer_available)
+def test_canny():
+    image = data.camera()
+    viewer = ImageViewer(image)
+    c = CannyPlugin()
+    viewer += c
+
+    canny_edges = viewer.show(False)
+    viewer.close()
+    edges = canny_edges[0][0]
+    assert edges.sum() == 2852
+
+
+@skipif(not viewer_available)
+def test_label_painter():
+    image = data.camera()
+    moon = data.moon()
+    viewer = ImageViewer(image)
+    lp = LabelPainter()
+    viewer += lp
+
+    assert_equal(lp.radius, 5)
+    lp.label = 1
+    assert_equal(str(lp.label), '1')
+    lp.label = 2
+    assert_equal(str(lp.paint_tool.label), '2')
+    assert_equal(lp.paint_tool.radius, 5)
+    lp._on_new_image(moon)
+    assert_equal(lp.paint_tool.shape, moon.shape)
+
+
+@skipif(not viewer_available)
+def test_crop():
+    image = data.camera()
+    viewer = ImageViewer(image)
+    c = Crop()
+    viewer += c
+
+    c.crop((0, 100, 0, 100))
+    assert_equal(viewer.image.shape, (101, 101))
+
+
+@skipif(not viewer_available)
+def test_color_histogram():
+    image = skimage.img_as_float(data.load('color.png'))
+    viewer = ImageViewer(image)
+    ch = ColorHistogram(dock='right')
+    viewer += ch
+
+    assert_almost_equal(viewer.image.std(), 0.352, 3),
+    ch.ab_selected((0, 100, 0, 100)),
+    assert_almost_equal(viewer.image.std(), 0.325, 3)
+
+
+@skipif(not viewer_available)
+def test_plot_plugin():
+    viewer = ImageViewer(data.moon())
+    plugin = PlotPlugin(image_filter=lambda x: x)
+    viewer += plugin
+
+    assert_equal(viewer.image, data.moon())
+    plugin._update_original_image(data.coins())
+    assert_equal(viewer.image, data.coins())
+    viewer.close()
+
+
+@skipif(not viewer_available)
+def test_plugin():
+    img = skimage.img_as_float(data.moon())
+    viewer = ImageViewer(img)
+
+    def median_filter(img, radius=3):
+        return median(img, selem=disk(radius=radius))
+
+    plugin = Plugin(image_filter=median_filter)
+    viewer += plugin
+
+    plugin += Slider('radius', 1, 5)
+
+    assert_almost_equal(np.std(viewer.image), 12.556, 3)
+
+    plugin.filter_image()
+
+    assert_almost_equal(np.std(viewer.image), 12.931, 3)
+
+    plugin.show()
+    plugin.close()
+    plugin.clean_up()
+    img, _ = plugin.output()
+    assert_equal(img, viewer.image)
diff --git a/skimage/viewer/tests/test_tools.py b/skimage/viewer/tests/test_tools.py
new file mode 100644
index 00000000..9f02e762
--- /dev/null
+++ b/skimage/viewer/tests/test_tools.py
@@ -0,0 +1,213 @@
+from collections import namedtuple
+
+import numpy as np
+from skimage import data
+from numpy.testing import assert_equal
+from numpy.testing.decorators import skipif
+
+try:
+    from skimage.viewer.qt import qt_api
+    from skimage.viewer import ImageViewer
+    from skimage.viewer.canvastools import (
+        LineTool, ThickLineTool, RectangleTool, PaintTool)
+    from skimage.viewer.canvastools.base import CanvasToolBase
+    viewer_available = not qt_api is None
+except ImportError:
+    viewer_available = False
+
+
+def get_end_points(image):
+    h, w = image.shape[0:2]
+    x = [w / 3, 2 * w / 3]
+    y = [h / 2] * 2
+    return np.transpose([x, y])
+
+
+def create_mouse_event(ax, button=1, xdata=0, ydata=0, key=None):
+    """
+     *name*
+        the event name
+
+    *canvas*
+        the FigureCanvas instance generating the event
+
+    *guiEvent*
+        the GUI event that triggered the matplotlib event
+
+    *x*
+        x position - pixels from left of canvas
+
+    *y*
+        y position - pixels from bottom of canvas
+
+    *inaxes*
+        the :class:`~matplotlib.axes.Axes` instance if mouse is over axes
+
+    *xdata*
+        x coord of mouse in data coords
+
+    *ydata*
+        y coord of mouse in data coords
+
+     *button*
+        button pressed None, 1, 2, 3, 'up', 'down' (up and down are used
+        for scroll events)
+
+    *key*
+        the key depressed when the mouse event triggered (see
+        :class:`KeyEvent`)
+
+    *step*
+        number of scroll steps (positive for 'up', negative for 'down')
+    """
+    event = namedtuple('Event',
+                       ('name canvas guiEvent x y inaxes xdata ydata '
+                        'button key step'))
+    event.button = button
+    event.x, event.y = ax.transData.transform((xdata, ydata))
+    event.xdata, event.ydata = xdata, ydata
+    event.inaxes = ax
+    event.canvas = ax.figure.canvas
+    event.key = key
+    event.step = 1
+    event.guiEvent = None
+    event.name = 'Custom'
+    return event
+
+
+@skipif(not viewer_available)
+def test_line_tool():
+    img = data.camera()
+    viewer = ImageViewer(img)
+
+    tool = LineTool(viewer.ax, maxdist=10)
+    tool.end_points = get_end_points(img)
+    assert_equal(tool.end_points, np.array([[170, 256], [341, 256]]))
+
+    # grab a handle and move it
+    grab = create_mouse_event(viewer.ax, xdata=170, ydata=256)
+    tool.on_mouse_press(grab)
+    move = create_mouse_event(viewer.ax, xdata=180, ydata=260)
+    tool.on_move(move)
+    tool.on_mouse_release(move)
+    assert_equal(tool.geometry, np.array([[180, 260], [341, 256]]))
+
+    # create a new line
+    new = create_mouse_event(viewer.ax, xdata=10, ydata=10)
+    tool.on_mouse_press(new)
+    move = create_mouse_event(viewer.ax, xdata=100, ydata=100)
+    tool.on_move(move)
+    tool.on_mouse_release(move)
+    assert_equal(tool.geometry, np.array([[100, 100], [10, 10]]))
+
+
+@skipif(not viewer_available)
+def test_thick_line_tool():
+    img = data.camera()
+    viewer = ImageViewer(img)
+
+    tool = ThickLineTool(viewer.ax, maxdist=10)
+    tool.end_points = get_end_points(img)
+
+    scroll_up = create_mouse_event(viewer.ax, button='up')
+    tool.on_scroll(scroll_up)
+    assert_equal(tool.linewidth, 2)
+
+    scroll_down = create_mouse_event(viewer.ax, button='down')
+    tool.on_scroll(scroll_down)
+    assert_equal(tool.linewidth, 1)
+
+    key_up = create_mouse_event(viewer.ax, key='+')
+    tool.on_key_press(key_up)
+    assert_equal(tool.linewidth, 2)
+
+    key_down = create_mouse_event(viewer.ax, key='-')
+    tool.on_key_press(key_down)
+    assert_equal(tool.linewidth, 1)
+
+
+@skipif(not viewer_available)
+def test_rect_tool():
+    img = data.camera()
+    viewer = ImageViewer(img)
+
+    tool = RectangleTool(viewer.ax, maxdist=10)
+    tool.extents = (100, 150, 100, 150)
+
+    assert_equal(tool.corners,
+                 ((100, 150, 150, 100), (100, 100, 150, 150)))
+    assert_equal(tool.extents, (100, 150, 100, 150))
+    assert_equal(tool.edge_centers,
+                 ((100, 125.0, 150, 125.0), (125.0, 100, 125.0, 150)))
+    assert_equal(tool.geometry, (100, 150, 100, 150))
+
+    # grab a corner and move it
+    grab = create_mouse_event(viewer.ax, xdata=100, ydata=100)
+    tool.press(grab)
+    move = create_mouse_event(viewer.ax, xdata=120, ydata=120)
+    tool.onmove(move)
+    tool.release(move)
+    assert_equal(tool.geometry, [120, 150, 120, 150])
+
+    # create a new line
+    new = create_mouse_event(viewer.ax, xdata=10, ydata=10)
+    tool.press(new)
+    move = create_mouse_event(viewer.ax, xdata=100, ydata=100)
+    tool.onmove(move)
+    tool.release(move)
+    assert_equal(tool.geometry, [10, 100,  10, 100])
+
+
+@skipif(not viewer_available)
+def test_paint_tool():
+    img = data.moon()
+    viewer = ImageViewer(img)
+
+    tool = PaintTool(viewer.ax, img.shape)
+
+    tool.radius = 10
+    assert_equal(tool.radius, 10)
+    tool.label = 2
+    assert_equal(tool.label, 2)
+    assert_equal(tool.shape, img.shape)
+
+    start = create_mouse_event(viewer.ax, xdata=100, ydata=100)
+    tool.on_mouse_press(start)
+    move = create_mouse_event(viewer.ax, xdata=110, ydata=110)
+    tool.on_move(move)
+    tool.on_mouse_release(move)
+    assert_equal(tool.overlay[tool.overlay == 2].size, 761)
+
+    tool.label = 5
+    start = create_mouse_event(viewer.ax, xdata=20, ydata=20)
+    tool.on_mouse_press(start)
+    move = create_mouse_event(viewer.ax, xdata=40, ydata=40)
+    tool.on_move(move)
+    tool.on_mouse_release(move)
+    assert_equal(tool.overlay[tool.overlay == 5].size, 881)
+    assert_equal(tool.overlay[tool.overlay == 2].size, 761)
+
+    enter = create_mouse_event(viewer.ax, key='enter')
+    tool.on_mouse_press(enter)
+
+    tool.overlay = tool.overlay * 0
+    assert_equal(tool.overlay.sum(), 0)
+
+
+@skipif(not viewer_available)
+def test_base_tool():
+    img = data.moon()
+    viewer = ImageViewer(img)
+
+    tool = CanvasToolBase(viewer.ax)
+    tool.set_visible(False)
+    tool.set_visible(True)
+
+    enter = create_mouse_event(viewer.ax, key='enter')
+    tool._on_key_press(enter)
+
+    tool.redraw()
+    tool.remove()
+
+    tool = CanvasToolBase(viewer.ax, useblit=False)
+    tool.redraw()
diff --git a/skimage/viewer/tests/test_utils.py b/skimage/viewer/tests/test_utils.py
new file mode 100644
index 00000000..30d74a51
--- /dev/null
+++ b/skimage/viewer/tests/test_utils.py
@@ -0,0 +1,43 @@
+# -*- coding: utf-8 -*-
+from numpy.testing.decorators import skipif
+
+try:
+    from skimage.viewer.qt import qt_api, QtCore, QtGui
+    from skimage.viewer import utils
+    from skimage.viewer.utils import dialogs
+except ImportError:
+    qt_api = None
+
+
+@skipif(qt_api is None)
+def test_event_loop():
+    utils.init_qtapp()
+    timer = QtCore.QTimer()
+    timer.singleShot(10, QtGui.QApplication.quit)
+    utils.start_qtapp()
+
+
+@skipif(qt_api is None)
+def test_format_filename():
+    fname = dialogs._format_filename(('apple', 2))
+    assert fname == 'apple'
+    fname = dialogs._format_filename('')
+    assert fname is None
+
+
+@skipif(qt_api is None)
+def test_open_file_dialog():
+    utils.init_qtapp()
+    timer = QtCore.QTimer()
+    timer.singleShot(10, QtGui.QApplication.quit)
+    filename = dialogs.open_file_dialog()
+    assert filename is None
+
+
+@skipif(qt_api is None)
+def test_save_file_dialog():
+    utils.init_qtapp()
+    timer = QtCore.QTimer()
+    timer.singleShot(10, QtGui.QApplication.quit)
+    filename = dialogs.save_file_dialog()
+    assert filename is None
diff --git a/skimage/viewer/tests/test_viewer.py b/skimage/viewer/tests/test_viewer.py
index 7fa4e374..cd6c7acb 100644
--- a/skimage/viewer/tests/test_viewer.py
+++ b/skimage/viewer/tests/test_viewer.py
@@ -1,48 +1,83 @@
-import skimage
-import skimage.data as data
-from skimage.viewer import ImageViewer
-from skimage.viewer.qt import qt_api
-from numpy.testing import assert_equal, assert_allclose
+
+from skimage import data
+from skimage.transform import pyramid_gaussian
+from skimage.filter import sobel
+from numpy.testing import assert_equal
 from numpy.testing.decorators import skipif
 
-
-def setup_line_profile(image):
-    from skimage.viewer.plugins.lineprofile import LineProfile
-    viewer = ImageViewer(skimage.img_as_float(image))
-    plugin = LineProfile()
-    viewer += plugin
-    return plugin
+try:
+    from skimage.viewer.qt import qt_api, QtGui, QtCore
+    from skimage.viewer.plugins import OverlayPlugin
+    from skimage.viewer.plugins.overlayplugin import recent_mpl_version
+    from skimage.viewer import ImageViewer, CollectionViewer
+    viewer_available = not qt_api is None
+except ImportError:
+    viewer_available = False
 
 
-@skipif(qt_api is None)
-def test_line_profile():
-    """ Test a line profile using an ndim=2 image"""
-    plugin = setup_line_profile(data.camera())
-    line_image, scan_data = plugin.output()
-    for inp in [line_image.nonzero()[0].size,
-                line_image.sum() / line_image.max(),
-                scan_data.size]:
-        assert_equal(inp, 172)
-    assert_equal(line_image.shape, (512, 512))
-    assert_allclose(scan_data.max(), 0.9139, rtol=1e-3)
-    assert_allclose(scan_data.mean(), 0.2828, rtol=1e-3)
+@skipif(not viewer_available)
+def test_viewer():
+    lena = data.lena()
+    coins = data.coins()
+
+    view = ImageViewer(lena)
+    import tempfile
+    _, filename = tempfile.mkstemp(suffix='.png')
+
+    view.show(False)
+    view.close()
+    view.save_to_file(filename)
+    view.open_file(filename)
+    assert_equal(view.image, lena)
+    view.image = coins
+    assert_equal(view.image, coins),
+    view.save_to_file(filename),
+    view.open_file(filename),
+    view.reset_image(),
+    assert_equal(view.image, coins)
 
 
-@skipif(qt_api is None)
-def test_line_profile_rgb():
-    """ Test a line profile using an ndim=3 image"""
-    plugin = setup_line_profile(data.chelsea())
-    for i in range(6):
-        plugin.line_tool._thicken_scan_line()
-    line_image, scan_data = plugin.output()
-    assert_equal(line_image[line_image == 128].size, 755)
-    assert_equal(line_image[line_image == 255].size, 151)
-    assert_equal(line_image.shape, (300, 451))
-    assert_equal(scan_data.shape, (152, 3))
-    assert_allclose(scan_data.max(), 0.772, rtol=1e-3)
-    assert_allclose(scan_data.mean(), 0.4355, rtol=1e-3)
+def make_key_event(key):
+    return QtGui.QKeyEvent(QtCore.QEvent.KeyPress, key,
+                           QtCore.Qt.NoModifier)
+
+
+@skipif(not viewer_available)
+def test_collection_viewer():
+
+    img = data.lena()
+    img_collection = tuple(pyramid_gaussian(img))
+
+    view = CollectionViewer(img_collection)
+    make_key_event(48)
+
+    view.update_index('', 2),
+    assert_equal(view.image, img_collection[2])
+    view.keyPressEvent(make_key_event(53))
+    assert_equal(view.image, img_collection[5])
+    view._format_coord(10, 10)
+
+
+@skipif(not viewer_available or not recent_mpl_version())
+def test_viewer_with_overlay():
+    img = data.coins()
+    ov = OverlayPlugin(image_filter=sobel)
+    viewer = ImageViewer(img)
+    viewer += ov
+
+    import tempfile
+    _, filename = tempfile.mkstemp(suffix='.png')
+
+    ov.color = 2
+    assert_equal(ov.color, 'yellow')
+    viewer.save_to_file(filename)
+    ov.display_filtered_image(img)
+    assert_equal(ov.overlay, img)
+    ov.overlay = None
+    assert_equal(ov.overlay, None)
+    ov.overlay = img
+    assert_equal(ov.overlay, img)
+    assert_equal(ov.filtered_image, img)
+
 
 
-if __name__ == "__main__":
-    from numpy.testing import run_module_suite
-    run_module_suite()
diff --git a/skimage/viewer/tests/test_widgets.py b/skimage/viewer/tests/test_widgets.py
new file mode 100644
index 00000000..aeb4ede2
--- /dev/null
+++ b/skimage/viewer/tests/test_widgets.py
@@ -0,0 +1,109 @@
+
+import os
+from skimage import data, img_as_float, io
+from numpy.testing import assert_almost_equal, assert_equal
+from numpy.testing.decorators import skipif
+
+try:
+    from skimage.viewer.qt import qt_api, QtGui, QtCore
+    from skimage.viewer import ImageViewer
+    from skimage.viewer.widgets import (
+        Slider, OKCancelButtons, SaveButtons, ComboBox, Text)
+    from skimage.viewer.plugins.base import Plugin
+    viewer_available = not qt_api is None
+except ImportError:
+    viewer_available = False
+
+
+def get_image_viewer():
+    image = data.coins()
+    viewer = ImageViewer(img_as_float(image))
+    viewer += Plugin()
+    return viewer
+
+
+@skipif(not viewer_available)
+def test_combo_box():
+    viewer = get_image_viewer()
+    cb = ComboBox('hello', ('a', 'b', 'c'))
+    viewer.plugins[0] += cb
+
+    assert_equal(str(cb.val), 'a')
+    assert_equal(cb.index, 0)
+    cb.index = 2
+    assert_equal(str(cb.val), 'c'),
+    assert_equal(cb.index, 2)
+
+
+@skipif(not viewer_available)
+def test_text_widget():
+    viewer = get_image_viewer()
+    txt = Text('hello', 'hello, world!')
+    viewer.plugins[0] += txt
+
+    assert_equal(str(txt.text), 'hello, world!')
+    txt.text = 'goodbye, world!'
+    assert_equal(str(txt.text), 'goodbye, world!')
+
+
+@skipif(not viewer_available)
+def test_slider_int():
+    viewer = get_image_viewer()
+    sld = Slider('radius', 2, 10, value_type='int')
+    viewer.plugins[0] += sld
+
+    assert_equal(sld.val, 4)
+    sld.val = 6
+    assert_equal(sld.val, 6)
+    sld.editbox.setText('5')
+    sld._on_editbox_changed()
+    assert_equal(sld.val, 5)
+
+
+@skipif(not viewer_available)
+def test_slider_float():
+    viewer = get_image_viewer()
+    sld = Slider('alpha', 2.1, 3.1, value=2.1, value_type='float',
+                 orientation='vertical', update_on='move')
+    viewer.plugins[0] += sld
+
+    assert_equal(sld.val, 2.1)
+    sld.val = 2.5
+    assert_almost_equal(sld.val, 2.5, 2)
+    sld.editbox.setText('0.1')
+    sld._on_editbox_changed()
+    assert_almost_equal(sld.val, 2.5, 2)
+
+
+@skipif(not viewer_available)
+def test_save_buttons():
+    viewer = get_image_viewer()
+    sv = SaveButtons()
+    viewer.plugins[0] += sv
+
+    import tempfile
+    _, filename = tempfile.mkstemp(suffix='.png')
+    os.remove(filename)
+
+    timer = QtCore.QTimer()
+    timer.singleShot(100, lambda: QtGui.QApplication.quit())
+
+    sv.save_to_stack()
+    sv.save_to_file(filename)
+
+    img = img_as_float(data.imread(filename))
+    assert_almost_equal(img, viewer.image)
+
+    img = io.pop()
+    assert_almost_equal(img, viewer.image)
+
+
+@skipif(not viewer_available)
+def test_ok_buttons():
+    viewer = get_image_viewer()
+    ok = OKCancelButtons()
+    viewer.plugins[0] += ok
+
+    ok.update_original_image(),
+    ok.close_plugin()
+
diff --git a/skimage/viewer/viewers/core.py b/skimage/viewer/viewers/core.py
index 32c10cd4..476017ef 100644
--- a/skimage/viewer/viewers/core.py
+++ b/skimage/viewer/viewers/core.py
@@ -174,9 +174,10 @@ class ImageViewer(QtGui.QMainWindow):
         h = viewer_size.height()
         self.resize(w + dx, h + dy)
 
-    def open_file(self):
+    def open_file(self, filename=None):
         """Open image file and display in viewer."""
-        filename = dialogs.open_file_dialog()
+        if filename is None:
+            filename = dialogs.open_file_dialog()
         if filename is None:
             return
         image = io.imread(filename)
@@ -187,7 +188,7 @@ class ImageViewer(QtGui.QMainWindow):
         self.image = image.copy()       # update displayed image
         self.original_image_changed.emit(image)
 
-    def save_to_file(self):
+    def save_to_file(self, filename=None):
         """Save current image to file.
 
         The current behavior is not ideal: It saves the image displayed on
@@ -195,7 +196,8 @@ class ImageViewer(QtGui.QMainWindow):
         not preserved (resizing the viewer window will alter the size of the
         saved image).
         """
-        filename = dialogs.save_file_dialog()
+        if filename is None:
+            filename = dialogs.save_file_dialog()
         if filename is None:
             return
         if len(self.ax.images) == 1:
diff --git a/skimage/viewer/widgets/core.py b/skimage/viewer/widgets/core.py
index 2bbf53d2..74fe9de4 100644
--- a/skimage/viewer/widgets/core.py
+++ b/skimage/viewer/widgets/core.py
@@ -244,7 +244,7 @@ class ComboBox(BaseWidget):
 
     @property
     def val(self):
-        return self._combo_box.value()
+        return self._combo_box.currentText()
 
     @property
     def index(self):
diff --git a/skimage/viewer/widgets/history.py b/skimage/viewer/widgets/history.py
index ce20b559..d1df8689 100644
--- a/skimage/viewer/widgets/history.py
+++ b/skimage/viewer/widgets/history.py
@@ -81,8 +81,9 @@ class SaveButtons(BaseWidget):
             NOTE: The io stack only works in interactive sessions.''')
         notify(msg)
 
-    def save_to_file(self):
-        filename = dialogs.save_file_dialog()
+    def save_to_file(self, filename=None):
+        if filename is None:
+            filename = dialogs.save_file_dialog()
         if filename is None:
             return
         image = self.plugin.filtered_image