diff --git a/jdaviz/configs/imviz/helper.py b/jdaviz/configs/imviz/helper.py
index 65fd8418f4..b1d293bbea 100644
--- a/jdaviz/configs/imviz/helper.py
+++ b/jdaviz/configs/imviz/helper.py
@@ -220,7 +220,7 @@ def zoom_level(self):
 
         """
         viewer = self.app.get_viewer("viewer-1")
-        if viewer.shape is None:
+        if viewer.shape is None:  # pragma: no cover
             raise ValueError('Viewer is still loading, try again later')
 
         screenx = viewer.shape[1]
@@ -240,7 +240,7 @@ def zoom_level(self, val):
         viewer = self.app.get_viewer("viewer-1")
         image = viewer.state.reference_data
         if (image is None or viewer.shape is None or
-                viewer.state.x_att is None or viewer.state.y_att is None):
+                viewer.state.x_att is None or viewer.state.y_att is None):  # pragma: no cover
             return
 
         # Zoom on X and Y will auto-adjust.
diff --git a/jdaviz/configs/imviz/tests/test_astrowidgets_api.py b/jdaviz/configs/imviz/tests/test_astrowidgets_api.py
index 7c534acea8..f5f8331301 100644
--- a/jdaviz/configs/imviz/tests/test_astrowidgets_api.py
+++ b/jdaviz/configs/imviz/tests/test_astrowidgets_api.py
@@ -65,6 +65,59 @@ def test_center_offset_sky(self):
             self.imviz.offset_by(dsky, dsky)
 
 
+class TestZoom(BaseImviz_WCS_NoWCS):
+
+    @pytest.mark.parametrize('val', (0, -0.1, 'foo', [1, 2]))
+    def test_invalid_zoom_level(self, val):
+        with pytest.raises(ValueError, match='Unsupported zoom level'):
+            self.imviz.zoom_level = val
+
+    def test_invalid_zoom(self):
+        with pytest.raises(ValueError, match='zoom only accepts int or float'):
+            self.imviz.zoom('fit')
+
+    def assert_zoom_results(self, zoom_level, x_min, x_max, y_min, y_max, dpix):
+        assert_allclose(self.imviz.zoom_level, zoom_level)
+        assert_allclose((self.viewer.state.x_min, self.viewer.state.x_max,
+                         self.viewer.state.y_min, self.viewer.state.y_max),
+                        (x_min + dpix, x_max + dpix,
+                         y_min + dpix, y_max + dpix))
+
+    @pytest.mark.parametrize('is_offcenter', (False, True))
+    def test_zoom(self, is_offcenter):
+        if is_offcenter:
+            self.imviz.center_on((0, 0))
+            dpix = -4.5
+        else:
+            self.imviz.center_on((4.5, 4.5))
+            dpix = 0
+
+        self.assert_zoom_results(10, -0.5, 9.5, -0.5, 9.5, dpix)
+
+        # NOTE: Not sure why X/Y min/max not exactly the same as aspect ratio 1
+        self.imviz.zoom_level = 1
+        self.assert_zoom_results(1, -46, 54, -45.5, 54.5, dpix)
+
+        self.imviz.zoom_level = 2
+        self.assert_zoom_results(2, -21.5, 28.5, -20.5, 29.5, dpix)
+
+        self.imviz.zoom(2)
+        self.assert_zoom_results(4, -9.5, 15.5, -8.0, 17.0, dpix)
+
+        self.imviz.zoom(0.5)
+        self.assert_zoom_results(2, -22.5, 27.5, -20.5, 29.5, dpix)
+
+        self.imviz.zoom_level = 0.5
+        self.assert_zoom_results(0.5, -98, 102, -95.5, 104.5, dpix)
+
+        # This fits the whole image on screen, regardless.
+        # NOTE: But somehow Y min/max auto-adjust does not work properly
+        # in the unit test when off-center. Works in notebook though.
+        if not is_offcenter:
+            self.imviz.zoom_level = 'fit'
+            self.assert_zoom_results(10, -0.5, 9.5, -0.5, 9.5, 0)
+
+
 class TestMarkers(BaseImviz_WCS_NoWCS):
 
     def test_invalid_markers(self):
diff --git a/jdaviz/configs/imviz/tests/utils.py b/jdaviz/configs/imviz/tests/utils.py
index 28cf0531ad..a69bb386a8 100644
--- a/jdaviz/configs/imviz/tests/utils.py
+++ b/jdaviz/configs/imviz/tests/utils.py
@@ -1,38 +1,42 @@
-import numpy as np
-import pytest
-from astropy.io import fits
-from astropy.wcs import WCS
-
-__all__ = ['BaseImviz_WCS_NoWCS']
-
-
-class BaseImviz_WCS_NoWCS:
-    @pytest.fixture(autouse=True)
-    def setup_class(self, imviz_app):
-        hdu = fits.ImageHDU(np.zeros((10, 10)), name='SCI')
-
-        # Apply some celestial WCS from
-        # https://learn.astropy.org/rst-tutorials/celestial_coords1.html
-        hdu.header.update({'CTYPE1': 'RA---TAN',
-                           'CUNIT1': 'deg',
-                           'CDELT1': -0.0002777777778,
-                           'CRPIX1': 1,
-                           'CRVAL1': 337.5202808,
-                           'NAXIS1': 10,
-                           'CTYPE2': 'DEC--TAN',
-                           'CUNIT2': 'deg',
-                           'CDELT2': 0.0002777777778,
-                           'CRPIX2': 1,
-                           'CRVAL2': -20.833333059999998,
-                           'NAXIS2': 10})
-
-        # Data with WCS
-        imviz_app.load_data(hdu, data_label='has_wcs')
-
-        # Data without WCS
-        imviz_app.load_data(hdu, data_label='no_wcs')
-        imviz_app.app.data_collection[1].coords = None
-
-        self.wcs = WCS(hdu.header)
-        self.imviz = imviz_app
-        self.viewer = imviz_app.app.get_viewer('viewer-1')
+import numpy as np
+import pytest
+from astropy.io import fits
+from astropy.wcs import WCS
+
+__all__ = ['BaseImviz_WCS_NoWCS']
+
+
+class BaseImviz_WCS_NoWCS:
+    @pytest.fixture(autouse=True)
+    def setup_class(self, imviz_app):
+        hdu = fits.ImageHDU(np.zeros((10, 10)), name='SCI')
+
+        # Apply some celestial WCS from
+        # https://learn.astropy.org/rst-tutorials/celestial_coords1.html
+        hdu.header.update({'CTYPE1': 'RA---TAN',
+                           'CUNIT1': 'deg',
+                           'CDELT1': -0.0002777777778,
+                           'CRPIX1': 1,
+                           'CRVAL1': 337.5202808,
+                           'NAXIS1': 10,
+                           'CTYPE2': 'DEC--TAN',
+                           'CUNIT2': 'deg',
+                           'CDELT2': 0.0002777777778,
+                           'CRPIX2': 1,
+                           'CRVAL2': -20.833333059999998,
+                           'NAXIS2': 10})
+
+        # Data with WCS
+        imviz_app.load_data(hdu, data_label='has_wcs')
+
+        # Data without WCS
+        imviz_app.load_data(hdu, data_label='no_wcs')
+        imviz_app.app.data_collection[1].coords = None
+
+        self.wcs = WCS(hdu.header)
+        self.imviz = imviz_app
+        self.viewer = imviz_app.app.get_viewer('viewer-1')
+
+        # Since we are not really displaying, need this to test zoom.
+        self.viewer.shape = (100, 100)
+        self.viewer.state._set_axes_aspect_ratio(1)