Make DegeneracyHunter tests more robust wrt different solutions (#1360

)

* Improving tests for degeneracy hunter

* Restore SCIP installation step w/o version pinning in setup-idaes Action

.github/actions/setup-idaes/action.yml

@@ -8,10 +8,10 @@ inputs:
     description: 'Command to use to install `install-target`'
     required: false
     default: pip --no-cache-dir install --progress-bar off
-  ampl-scip-version:
-    description: Version of AMPL Scip solver to install
+  ampl-scip-pip-target:
+    description: pip install target (dist name and optionally version constraint) of AMPL SCIP solver to install
     required: false
-    default: '20240121'
+    default: ampl-module-scip
 runs:
   using: "composite"
   steps:
@@ -46,9 +46,10 @@ runs:
         echo '::group::Output of "idaes get-extensions" command'
         idaes get-extensions --extra petsc --verbose
         echo '::endgroup::'
-    - name: Install SCIP from AMPL
+    - name: Install AMPL SCIP (${{ inputs.ampl-scip-pip-target }})
+      if: inputs.ampl-scip-pip-target
       shell: bash -l {0}
       run: |
         echo '::group::Output of "pip install ampl_module_scip" command'
-        ${{ inputs.install-command }} --index-url https://pypi.ampl.com ampl_module_scip==${{ inputs.ampl-scip-version }}
+        ${{ inputs.install-command }} --index-url https://pypi.ampl.com ${{ inputs.ampl-scip-pip-target }}
         echo '::endgroup::'

idaes/core/util/tests/test_model_diagnostics.py

@@ -1974,23 +1974,32 @@ def test_solve_candidates_milp(self, model, scip_solver):
         dh._prepare_candidates_milp()
         dh._solve_candidates_milp()
 
-        assert value(dh.candidates_milp.nu[0]) == pytest.approx(1e-05, rel=1e-5)
-        assert value(dh.candidates_milp.nu[1]) == pytest.approx(-1e-05, rel=1e-5)
+        assert dh.degenerate_set == {
+            model.con2: value(dh.candidates_milp.nu[0]),
+            model.con5: value(dh.candidates_milp.nu[1]),
+        }
+
+        assert abs(value(dh.candidates_milp.nu[0])) == pytest.approx(1e-05, rel=1e-5)
+        assert abs(value(dh.candidates_milp.nu[1])) == pytest.approx(1e-05, rel=1e-5)
 
-        assert value(dh.candidates_milp.y_pos[0]) == pytest.approx(0, abs=1e-5)
-        assert value(dh.candidates_milp.y_pos[1]) == pytest.approx(0, rel=1e-5)
+        # One must be positive and one must be negative, so produce will be negative
+        assert value(
+            dh.candidates_milp.nu[0] * dh.candidates_milp.nu[1]
+        ) == pytest.approx(-1e-10, rel=1e-5)
 
-        assert value(dh.candidates_milp.y_neg[0]) == pytest.approx(0, abs=1e-5)
-        assert value(dh.candidates_milp.y_neg[1]) == pytest.approx(1, abs=1e-5)
+        assert (
+            value(
+                dh.candidates_milp.y_pos[0]
+                + dh.candidates_milp.y_pos[1]
+                + dh.candidates_milp.y_neg[0]
+                + dh.candidates_milp.y_neg[1]
+            )
+            >= 1
+        )
 
         assert value(dh.candidates_milp.abs_nu[0]) == pytest.approx(1e-05, rel=1e-5)
         assert value(dh.candidates_milp.abs_nu[1]) == pytest.approx(1e-05, rel=1e-5)
 
-        assert dh.degenerate_set == {
-            model.con2: value(dh.candidates_milp.nu[0]),
-            model.con5: value(dh.candidates_milp.nu[1]),
-        }
-
     @pytest.mark.unit
     def test_prepare_ids_milp(self, model):
         dh = DegeneracyHunter2(model)