Add tests for flow vs OMP_NUM_THREADS

tests/ert/ui_tests/cli/test_run_flow_simulator.py

@@ -128,6 +128,39 @@ def test_ert_will_fetch_parallel_keyword_and_set_mpi_processes():
     assert re.search(r"Threads per MPI process:\s+1", flow_stdout)
 
 
+@pytest.mark.usefixtures("eightcells")
+@pytest.mark.skipif(not shutil.which("flowrun"), reason="flowrun not available")
+@pytest.mark.parametrize("num_cpu", [1, 2])
+def test_flow_will_always_obey_omp_num_threads_also_when_mpi_is_active(num_cpu):
+    """This part of flow Ert cannot control, and this scenario should thus be
+    avoided. However, if the users use SETENV manually it will happen.
+    SETENV takes precedence over plugin env configuration so configuriation of
+    the FLOW forward model through plugins will not help either."""
+    deck = Path("EIGHTCELLS.DATA").read_text(encoding="utf-8")
+    assert "PARALLEL" not in deck
+    Path("flow.ert").write_text(
+        dedent(f"""
+    NUM_REALIZATIONS 1
+    ECLBASE EIGHTCELLS
+    NUM_CPU {num_cpu}
+    DATA_FILE EIGHTCELLS.DATA
+    SETENV OMP_NUM_THREADS 2
+    RUNPATH realization-<IENS>
+    FORWARD_MODEL FLOW()
+    """).strip(),
+        encoding="utf-8",
+    )
+
+    run_cli(TEST_RUN_MODE, "--disable-monitoring", "flow.ert")
+    flow_stdout = Path("realization-0/FLOW.stdout.0").read_text(encoding="utf-8")
+    assert (
+        "Warning: Environment variable OMP_NUM_THREADS takes precedence over the --threads-per-process"
+        in flow_stdout
+    )
+    assert re.search(rf"Number of MPI processes:\s+{num_cpu}", flow_stdout)
+    assert re.search(r"Threads per MPI process:\s+2", flow_stdout)
+
+
 @pytest.mark.usefixtures("eightcells")
 @pytest.mark.skipif(not shutil.which("flowrun"), reason="flowrun not available")
 def test_num_cpu_wins_over_parallel_in_deck():