fix loadFile for package.mo: don't copy it out of its package directory

OMPython/modelica_system_omc.py

@@ -140,15 +140,24 @@ def model(
             if not file_path.is_file():
                 raise IOError(f"Model file {file_path} does not exist!")
 
-            self._file_name = self.getWorkDirectory() / file_path.name
-            if (isinstance(self._session, OMCSessionLocal)
-                    and file_path.as_posix() == self._file_name.as_posix()):
-                pass
-            elif self._file_name.is_file():
-                raise IOError(f"Simulation model file {self._file_name} exist - not overwriting!")
+            if isinstance(self._session, OMCSessionLocal) and file_path.name == "package.mo":
+                # Structured/directory-based package: OMC requires the enclosing
+                # directory's name to match the package name declared inside
+                # package.mo, and the package may span sibling .mo files in that
+                # same directory tree (e.g. Tests/StableBouncingBall.mo). Copying
+                # just this one file into a randomly-named work directory breaks
+                # both of those, so load it in place instead.
+                self._file_name = self._session.omcpath(file_path)
             else:
-                content = file_path.read_text(encoding='utf-8')
-                self._file_name.write_text(content)
+                self._file_name = self.getWorkDirectory() / file_path.name
+                if (isinstance(self._session, OMCSessionLocal)
+                        and file_path.as_posix() == self._file_name.as_posix()):
+                    pass
+                elif self._file_name.is_file():
+                    raise IOError(f"Simulation model file {self._file_name} exist - not overwriting!")
+                else:
+                    content = file_path.read_text(encoding='utf-8')
+                    self._file_name.write_text(content)
 
         if self._file_name is not None:
             self._loadFile(fileName=self._file_name)

tests/resources/BouncingBalls/Tests/BouncingBall.mo

@@ -0,0 +1,22 @@
+within BouncingBalls.Tests;
+
+model BouncingBall "The 'classic' bouncing ball model"
+  type Height=Real(unit="m");
+  type Velocity=Real(unit="m/s");
+  parameter Real e=0.8 "Coefficient of restitution";
+  parameter Height h0=1.0 "Initial height";
+  Height h "Height";
+  Velocity v(start=0.0, fixed=true) "Velocity";
+initial equation
+  h = h0;
+equation
+  v = der(h);
+  der(v) = -9.81;
+  when h<0 then
+    reinit(v, -e*pre(v));
+  end when;
+annotation(
+      experiment(StartTime = 0, StopTime = 10, Tolerance = 1e-06, Interval = 0.01),
+      __OpenModelica_commandLineOptions = "--matchingAlgorithm=PFPlusExt --indexReductionMethod=dynamicStateSelection -d=initialization,NLSanalyticJacobian",
+      __OpenModelica_simulationFlags(lv = "LOG_STDOUT,LOG_ASSERT,LOG_STATS", s = "dassl", variableFilter = ".*"));
+end BouncingBall;

tests/resources/BouncingBalls/Tests/StableBouncingBall.mo

@@ -0,0 +1,27 @@
+within BouncingBalls.Tests;
+
+model StableBouncingBall
+  "The 'classic' bouncing ball model with numerical tolerances"
+  type Height=Real(unit="m");
+  type Velocity=Real(unit="m/s");
+  parameter Real e=0.8 "Coefficient of restitution";
+  parameter Height h0=1.0 "Initial height";
+  constant Height eps=1e-3 "Small height";
+  Boolean done "Flag when to turn off gravity";
+  Height h "Height";
+  Velocity v(start=0.0, fixed=true) "Velocity";
+initial equation
+  h = h0;
+  done = false;
+equation
+  v = der(h);
+  der(v) = if done then 0 else -9.81;
+  when {h<0,h<-eps} then
+    done = h<-eps;
+    reinit(v, -e*(if h<-eps then 0 else pre(v)));
+  end when;
+annotation(
+      experiment(StartTime = 0, StopTime = 10, Tolerance = 1e-06, Interval = 0.01),
+      __OpenModelica_commandLineOptions = "--matchingAlgorithm=PFPlusExt --indexReductionMethod=dynamicStateSelection -d=initialization,NLSanalyticJacobian",
+      __OpenModelica_simulationFlags(lv = "LOG_STDOUT,LOG_ASSERT,LOG_STATS", s = "dassl", variableFilter = ".*"));
+end StableBouncingBall;

tests/resources/BouncingBalls/Tests/package.mo

@@ -0,0 +1,8 @@
+within BouncingBalls;
+package Tests "Tests"
+  extends Modelica.Icons.Package;
+
+annotation (Documentation(info="<html>
+<p>This package contains testing models</p>
+</html>"));
+end Tests;

tests/resources/BouncingBalls/Tests/package.order

@@ -0,0 +1,2 @@
+BouncingBall
+StableBouncingBall

tests/resources/BouncingBalls/package.mo

@@ -0,0 +1,18 @@
+within ;
+package BouncingBalls "Test"
+  extends Modelica.Icons.Package;
+
+  annotation(version="0.0.1",
+    versionDate = "2026-09-18",
+    uses(Modelica(version = "4.1.0")),
+    preferredView = "info", Documentation(info = "<html>
+<h4>BouncingBalls</h4>
+
+<p>BouncingBall test package</p>
+
+<h4>Short description</h4>
+
+<p>BlaBla</p>
+</html>"));
+
+end BouncingBalls;

tests/resources/BouncingBalls/package.order

@@ -0,0 +1 @@
+Tests

tests/test_ModelicaSystemOMC.py

@@ -140,6 +140,23 @@ def test_relative_path(model_firstorder):
         model_file.unlink()  # clean up the temporary file
 
 
+def test_load_structured_package():
+    # Regression test for loading a directory-based package via its package.mo:
+    # OMC requires the enclosing directory's name to match the package name, and
+    # the package spans a sibling file in a nested subdirectory
+    # (Tests/StableBouncingBall.mo). Both break if package.mo gets copied out of
+    # its directory instead of being loaded in place.
+    package_dir = pathlib.Path(__file__).parent / "resources" / "BouncingBalls"
+
+    mod = OMPython.ModelicaSystemOMC()
+    mod.model(
+        model_file=package_dir / "package.mo",
+        model_name="BouncingBalls.Tests.StableBouncingBall",
+        libraries=["Modelica"],
+    )
+    mod.simulate()
+
+
 def test_customBuildDirectory(tmp_path, model_firstorder):
     tmpdir = tmp_path / "tmpdir1"
     tmpdir.mkdir()

tests/test_linearization.py

@@ -82,11 +82,10 @@ def test_getters(tmp_path):
     assert mod.getLinearInputs() == ["u1", "u2"]
     assert mod.getLinearStates() == ["omega", "phi"]
     assert mod.getLinearOutputs() == ["y1", "y2"]
-    assert np.isclose(A, [[0, param_g / param_l], [1, 0]]).all()
-    assert np.isclose(B, [[0, 0], [0, 1]]).all()
-    assert np.isclose(C, [[0.5, 1], [0, 1]]).all()
-    assert np.isclose(D, [[1, 0], [1, 0]]).all()
-
+    assert np.isclose(A, [[0, param_g / param_l], [1, 0]], atol=1e-10, rtol=1e-9).all()
+    assert np.isclose(B, [[0, 0], [0, 1]], atol=1e-10, rtol=1e-9).all()
+    assert np.isclose(C, [[0.5, 1], [0, 1]], atol=1e-10, rtol=1e-9).all()
+    assert np.isclose(D, [[1, 0], [1, 0]], atol=1e-10, rtol=1e-9).all()
     # test LinearizationResult
     result = mod.linearize()
     assert result[0] == A