Update test_simulate_experiment_to_events for antimony 3.1.0

In antimony>=3.1.0, initial values for substanceOnly species are interpreted as amounts.
Before, they were interpreted as concentrations.
Update `test_simulate_experiment_to_events` accordingly and require >=3.1.0 for tests.

Author: dweindl

pyproject.toml

@@ -36,7 +36,7 @@ maintainers = [
 
 [project.optional-dependencies]
 tests = [
-    "antimony>=2.14.0",
+    "antimony>=3.1.0",
     "copasi-basico>=0.85",
     "pysb",
     "pytest",

tests/v2/test_converters.py

@@ -96,11 +96,12 @@ def test_simulate_experiment_to_events():
     species s2c_comp1 in comp1 = 3
     species s2c_comp2 in comp2 = 4
     # amount-based species
-    # (note: the initial values are concentrations nonetheless)
-    substanceOnly species s3a_comp1 in comp1 = 5
-    substanceOnly species s3a_comp2 in comp2 = 6
-    substanceOnly species s4a_comp1 in comp1 = 7
-    substanceOnly species s4a_comp2 in comp2 = 8
+    # (note that in antimony<3.1.0 the initial values are concentrations
+    #  nonetheless)
+    substanceOnly species s3a_comp1 in comp1 = 5 * comp1
+    substanceOnly species s3a_comp2 in comp2 = 6 * comp2
+    substanceOnly species s4a_comp1 in comp1 = 7 * comp1
+    substanceOnly species s4a_comp2 in comp2 = 8 * comp2
 
     # something dynamic
     some_species in comp1 = 0