From e39d08fc65087c18b8d1b409d55c14cd66cdbb71 Mon Sep 17 00:00:00 2001
From: Dario Panici <dpanici@princeton.edu>
Date: Fri, 16 Aug 2024 10:42:54 -0400
Subject: [PATCH] improve error msg for plot coilis

---
 desc/plotting.py       | 8 ++++++++
 tests/test_plotting.py | 2 ++
 2 files changed, 10 insertions(+)

diff --git a/desc/plotting.py b/desc/plotting.py
index ba822a5b2b..478e11dc66 100644
--- a/desc/plotting.py
+++ b/desc/plotting.py
@@ -2384,6 +2384,8 @@ def plot_coils(coils, grid=None, fig=None, return_data=False, **kwargs):
         dictionary of the data plotted, only returned if ``return_data=True``
 
     """
+    from desc.coils import _Coil
+
     lw = kwargs.pop("lw", 5)
     ls = kwargs.pop("ls", "solid")
     figsize = kwargs.pop("figsize", (10, 10))
@@ -2394,6 +2396,12 @@ def plot_coils(coils, grid=None, fig=None, return_data=False, **kwargs):
         ValueError,
         f"plot_coils got unexpected keyword argument: {kwargs.keys()}",
     )
+    errorif(
+        not isinstance(coils, _Coil),
+        ValueError,
+        "Expected `coils` to be object of type `_Coil`, instead got type"
+        f" {type(coils)}",
+    )
 
     if not isinstance(lw, (list, tuple)):
         lw = [lw]
diff --git a/tests/test_plotting.py b/tests/test_plotting.py
index 8252d349d8..1351b46c93 100644
--- a/tests/test_plotting.py
+++ b/tests/test_plotting.py
@@ -801,6 +801,8 @@ def test_plot_coils():
     coil.rotate(angle=np.pi / N)
     coils = CoilSet.linspaced_angular(coil, I, [0, 0, 1], np.pi / NFP, N // NFP // 2)
     coils2 = MixedCoilSet.from_symmetry(coils, NFP, True)
+    with pytest.raises(ValueError, match="Expected `coils`"):
+        plot_coils("not a coil")
     fig, data = plot_coils(coils2, return_data=True)
 
     def flatten_coils(coilset):