fix: valueError also if no fov in GridWidthHeight (#142)

* fix: ValueError also for GridWidthHeight

* ci(dependabot): bump actions/checkout from 3 to 4 (#134)

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...v4)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

* refactor: remove __str__ method on MDASequence (#136)

* test: add napari-micromanager test (#139)

* test: add napari-micro test

* ci: fix deps

* test: fix

---------

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Talley Lambert <[email protected]>

src/useq/_grid.py

@@ -188,13 +188,15 @@ def _ncolumns(self, dx: float) -> int:
     def num_positions(self) -> int:
         """Return the number of individual positions in the grid.
 
-        Note: For GridFromEdges, this will depend on field of view size.  If no
-        field of view size is provided, the number of positions will be 1.
+        Note: For GridFromEdges and GridWidthHeight, this will depend on field of view
+        size. If no field of view size is provided, the number of positions will be 1.
         """
-        if not self.is_relative and (self.fov_width is None or self.fov_height is None):
+        if isinstance(self, (GridFromEdges, GridWidthHeight)) and (
+            self.fov_width is None or self.fov_height is None
+        ):
             raise ValueError(
-                "Retrieving the number of positions in a GridFromEdges plan requires "
-                "that the field of view size be set."
+                "Retrieving the number of positions in a GridFromEdges or "
+                "GridWidthHeight plan requires the field of view size to be set."
             )
 
         dx, dy = self._step_size(self.fov_width or 1, self.fov_height or 1)

tests/test_grid.py

@@ -99,9 +99,12 @@ def test_grid_type():
 
 
 def test_num_position_error() -> None:
-    with pytest.raises(ValueError, match="the field of view size be set"):
+    with pytest.raises(ValueError, match="plan requires the field of view size"):
         GridFromEdges(top=1, left=-1, bottom=-1, right=2).num_positions()
 
+    with pytest.raises(ValueError, match="plan requires the field of view size"):
+        GridWidthHeight(width=2, height=2).num_positions()
+
 
 expected_rectangle = [(0.2, 1.1), (0.4, 0.2), (-0.3, 0.7)]
 expected_ellipse = [(-0.0, -2.1), (0.7, 1.7), (-1.0, 1.3)]