diff --git a/pyproject.toml b/pyproject.toml
index 751c9085ec8..bdbfd9b52ab 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -175,7 +175,6 @@ module = [
   "xarray.tests.test_merge",
   "xarray.tests.test_missing",
   "xarray.tests.test_parallelcompat",
-  "xarray.tests.test_plot",
   "xarray.tests.test_sparse",
   "xarray.tests.test_ufuncs",
   "xarray.tests.test_units",
diff --git a/xarray/tests/test_plot.py b/xarray/tests/test_plot.py
index 7c28b1cd140..e636be5589f 100644
--- a/xarray/tests/test_plot.py
+++ b/xarray/tests/test_plot.py
@@ -3,7 +3,7 @@
 import contextlib
 import inspect
 import math
-from collections.abc import Hashable
+from collections.abc import Generator, Hashable
 from copy import copy
 from datetime import date, datetime, timedelta
 from typing import Any, Callable, Literal
@@ -85,44 +85,46 @@ def test_all_figures_closed():
 
 @pytest.mark.flaky
 @pytest.mark.skip(reason="maybe flaky")
-def text_in_fig():
+def text_in_fig() -> set[str]:
     """
     Return the set of all text in the figure
     """
-    return {t.get_text() for t in plt.gcf().findobj(mpl.text.Text)}
+    return {t.get_text() for t in plt.gcf().findobj(mpl.text.Text)}  # type: ignore[attr-defined] # mpl error?
 
 
-def find_possible_colorbars():
+def find_possible_colorbars() -> list[mpl.collections.QuadMesh]:
     # nb. this function also matches meshes from pcolormesh
-    return plt.gcf().findobj(mpl.collections.QuadMesh)
+    return plt.gcf().findobj(mpl.collections.QuadMesh)  # type: ignore[return-value] # mpl error?
 
 
-def substring_in_axes(substring, ax):
+def substring_in_axes(substring: str, ax: mpl.axes.Axes) -> bool:
     """
     Return True if a substring is found anywhere in an axes
     """
-    alltxt = {t.get_text() for t in ax.findobj(mpl.text.Text)}
+    alltxt: set[str] = {t.get_text() for t in ax.findobj(mpl.text.Text)}  # type: ignore[attr-defined] # mpl error?
     for txt in alltxt:
         if substring in txt:
             return True
     return False
 
 
-def substring_not_in_axes(substring, ax):
+def substring_not_in_axes(substring: str, ax: mpl.axes.Axes) -> bool:
     """
     Return True if a substring is not found anywhere in an axes
     """
-    alltxt = {t.get_text() for t in ax.findobj(mpl.text.Text)}
+    alltxt: set[str] = {t.get_text() for t in ax.findobj(mpl.text.Text)}  # type: ignore[attr-defined] # mpl error?
     check = [(substring not in txt) for txt in alltxt]
     return all(check)
 
 
-def property_in_axes_text(property, property_str, target_txt, ax):
+def property_in_axes_text(
+    property, property_str, target_txt, ax: mpl.axes.Axes
+) -> bool:
     """
     Return True if the specified text in an axes
     has the property assigned to property_str
     """
-    alltxt = ax.findobj(mpl.text.Text)
+    alltxt: list[mpl.text.Text] = ax.findobj(mpl.text.Text)  # type: ignore[assignment]
     check = []
     for t in alltxt:
         if t.get_text() == target_txt:
@@ -130,7 +132,7 @@ def property_in_axes_text(property, property_str, target_txt, ax):
     return all(check)
 
 
-def easy_array(shape, start=0, stop=1):
+def easy_array(shape: tuple[int, ...], start: float = 0, stop: float = 1) -> np.ndarray:
     """
     Make an array with desired shape using np.linspace
 
@@ -140,7 +142,7 @@ def easy_array(shape, start=0, stop=1):
     return a.reshape(shape)
 
 
-def get_colorbar_label(colorbar):
+def get_colorbar_label(colorbar) -> str:
     if colorbar.orientation == "vertical":
         return colorbar.ax.get_ylabel()
     else:
@@ -150,27 +152,27 @@ def get_colorbar_label(colorbar):
 @requires_matplotlib
 class PlotTestCase:
     @pytest.fixture(autouse=True)
-    def setup(self):
+    def setup(self) -> Generator:
         yield
         # Remove all matplotlib figures
         plt.close("all")
 
-    def pass_in_axis(self, plotmethod, subplot_kw=None):
+    def pass_in_axis(self, plotmethod, subplot_kw=None) -> None:
         fig, axs = plt.subplots(ncols=2, subplot_kw=subplot_kw)
         plotmethod(ax=axs[0])
         assert axs[0].has_data()
 
     @pytest.mark.slow
-    def imshow_called(self, plotmethod):
+    def imshow_called(self, plotmethod) -> bool:
         plotmethod()
         images = plt.gca().findobj(mpl.image.AxesImage)
         return len(images) > 0
 
-    def contourf_called(self, plotmethod):
+    def contourf_called(self, plotmethod) -> bool:
         plotmethod()
 
         # Compatible with mpl before (PathCollection) and after (QuadContourSet) 3.8
-        def matchfunc(x):
+        def matchfunc(x) -> bool:
             return isinstance(
                 x, (mpl.collections.PathCollection, mpl.contour.QuadContourSet)
             )
@@ -1248,14 +1250,16 @@ def test_discrete_colormap_list_levels_and_vmin_or_vmax(self) -> None:
     def test_discrete_colormap_provided_boundary_norm(self) -> None:
         norm = mpl.colors.BoundaryNorm([0, 5, 10, 15], 4)
         primitive = self.darray.plot.contourf(norm=norm)
-        np.testing.assert_allclose(primitive.levels, norm.boundaries)
+        np.testing.assert_allclose(list(primitive.levels), norm.boundaries)
 
     def test_discrete_colormap_provided_boundary_norm_matching_cmap_levels(
         self,
     ) -> None:
         norm = mpl.colors.BoundaryNorm([0, 5, 10, 15], 4)
         primitive = self.darray.plot.contourf(norm=norm)
-        assert primitive.colorbar.norm.Ncmap == primitive.colorbar.norm.N
+        cbar = primitive.colorbar
+        assert cbar is not None
+        assert cbar.norm.Ncmap == cbar.norm.N  # type: ignore[attr-defined] # Exists, debatable if public though.
 
 
 class Common2dMixin:
@@ -2532,7 +2536,7 @@ def test_default_labels(self) -> None:
 
         # Leftmost column should have array name
         for ax in g.axs[:, 0]:
-            assert substring_in_axes(self.darray.name, ax)
+            assert substring_in_axes(str(self.darray.name), ax)
 
     def test_test_empty_cell(self) -> None:
         g = (
@@ -2635,7 +2639,7 @@ def test_facetgrid(self) -> None:
             (True, "continuous", False, True),
         ],
     )
-    def test_add_guide(self, add_guide, hue_style, legend, colorbar):
+    def test_add_guide(self, add_guide, hue_style, legend, colorbar) -> None:
         meta_data = _infer_meta_data(
             self.ds,
             x="x",
@@ -2811,7 +2815,7 @@ def test_bad_args(
         add_legend: bool | None,
         add_colorbar: bool | None,
         error_type: type[Exception],
-    ):
+    ) -> None:
         with pytest.raises(error_type):
             self.ds.plot.scatter(
                 x=x, y=y, hue=hue, add_legend=add_legend, add_colorbar=add_colorbar
@@ -3011,20 +3015,22 @@ def test_ncaxis_notinstalled_line_plot(self) -> None:
 @requires_matplotlib
 class TestAxesKwargs:
     @pytest.fixture(params=[1, 2, 3])
-    def data_array(self, request):
+    def data_array(self, request) -> DataArray:
         """
         Return a simple DataArray
         """
         dims = request.param
         if dims == 1:
             return DataArray(easy_array((10,)))
-        if dims == 2:
+        elif dims == 2:
             return DataArray(easy_array((10, 3)))
-        if dims == 3:
+        elif dims == 3:
             return DataArray(easy_array((10, 3, 2)))
+        else:
+            raise ValueError(f"No DataArray implemented for {dims=}.")
 
     @pytest.fixture(params=[1, 2])
-    def data_array_logspaced(self, request):
+    def data_array_logspaced(self, request) -> DataArray:
         """
         Return a simple DataArray with logspaced coordinates
         """
@@ -3033,12 +3039,14 @@ def data_array_logspaced(self, request):
             return DataArray(
                 np.arange(7), dims=("x",), coords={"x": np.logspace(-3, 3, 7)}
             )
-        if dims == 2:
+        elif dims == 2:
             return DataArray(
                 np.arange(16).reshape(4, 4),
                 dims=("y", "x"),
                 coords={"x": np.logspace(-1, 2, 4), "y": np.logspace(-5, -1, 4)},
             )
+        else:
+            raise ValueError(f"No DataArray implemented for {dims=}.")
 
     @pytest.mark.parametrize("xincrease", [True, False])
     def test_xincrease_kwarg(self, data_array, xincrease) -> None:
@@ -3146,16 +3154,16 @@ def test_facetgrid_single_contour() -> None:
 
 
 @requires_matplotlib
-def test_get_axis_raises():
+def test_get_axis_raises() -> None:
     # test get_axis raises an error if trying to do invalid things
 
     # cannot provide both ax and figsize
     with pytest.raises(ValueError, match="both `figsize` and `ax`"):
-        get_axis(figsize=[4, 4], size=None, aspect=None, ax="something")
+        get_axis(figsize=[4, 4], size=None, aspect=None, ax="something")  # type: ignore[arg-type]
 
     # cannot provide both ax and size
     with pytest.raises(ValueError, match="both `size` and `ax`"):
-        get_axis(figsize=None, size=200, aspect=4 / 3, ax="something")
+        get_axis(figsize=None, size=200, aspect=4 / 3, ax="something")  # type: ignore[arg-type]
 
     # cannot provide both size and figsize
     with pytest.raises(ValueError, match="both `figsize` and `size`"):
@@ -3167,7 +3175,7 @@ def test_get_axis_raises():
 
     # cannot provide axis and subplot_kws
     with pytest.raises(ValueError, match="cannot use subplot_kws with existing ax"):
-        get_axis(figsize=None, size=None, aspect=None, ax=1, something_else=5)
+        get_axis(figsize=None, size=None, aspect=None, ax=1, something_else=5)  # type: ignore[arg-type]
 
 
 @requires_matplotlib