[Test] yaml2ck: Add test for phase with no reactions

The test case verifies that a phase with no reactions will successfully write to a Chemkin file.

test/data/yaml-ck-reactions.yaml

@@ -16,6 +16,15 @@ phases:
   state:
     T: 300.0
     P: 1.01325e+05
+- name: no-reactions
+  thermo: ideal-gas
+  elements: [O, H, Ar]
+  kinetics: gas
+  transport: mixture-averaged
+  reactions: none
+  state:
+    T: 300.0
+    P: 1.01325e+05
 
 species:
 - name: AR

test/python/test_convert.py

@@ -783,6 +783,16 @@ def test_yaml_2_ck_reactions(self):
         self.check_kinetics(ck_phase, yaml_phase, [900, 1800], [2e5, 20e5], tol=2e-7)
         self.check_transport(ck_phase, yaml_phase, [298, 1001, 2400])
 
+    def test_phase_no_reactions(self):
+        input_file = self.test_data_path / "yaml-ck-reactions.yaml"
+        yaml_phase = ct.Solution(input_file, name="no-reactions")
+        assert yaml_phase.n_reactions == 0
+
+        ck_file = self.test_work_path / 'no-reactions.ck'
+        ck_file.unlink(missing_ok=True)
+        yaml_phase.write_chemkin(ck_file, quiet=True)
+        assert ck_file.exists()
+
     def test_write_chemkin(self):
         # test alternative converter
         yaml_phase = ct.Solution('h2o2.yaml')