fix: restore original simple_refrig_api and platform path fixes

tests/test_diagram_api.py

@@ -0,0 +1,44 @@
+import base64
+import pytest
+from fastapi.testclient import TestClient
+
+from app.main import app
+
+client = TestClient(app)
+
+
+def test_diagram_json_no_image():
+    body = {
+        'refrigerant': 'R290',
+        'pressure_range': {'min': 0.1, 'max': 10.0},
+        'format': 'json',
+        'include_isotherms': True,
+        'width': 800,
+        'height': 600,
+        'dpi': 100
+    }
+    r = client.post('/api/v1/diagrams/ph', json=body)
+    assert r.status_code == 200
+    j = r.json()
+    # image key should not be present for json-only
+    assert 'image' not in j
+    assert 'data' in j
+
+
+def test_diagram_png_includes_image():
+    body = {
+        'refrigerant': 'R290',
+        'pressure_range': {'min': 0.1, 'max': 10.0},
+        'format': 'png',
+        'include_isotherms': True,
+        'width': 800,
+        'height': 600,
+        'dpi': 100
+    }
+    r = client.post('/api/v1/diagrams/ph', json=body)
+    assert r.status_code == 200
+    j = r.json()
+    assert 'image' in j
+    # Validate base64 decodes
+    decoded = base64.b64decode(j['image'])
+    assert len(decoded) > 10

tests/test_economizer_unit.py

@@ -0,0 +1,19 @@
+import sys, os
+ROOT = os.path.abspath(os.path.join(os.path.dirname(__file__), '..'))
+if ROOT not in sys.path:
+    sys.path.insert(0, ROOT)
+
+from app.core.refrigerant_loader import RefrigerantLibrary
+from app.services.cycle_calculator import CycleCalculator
+
+
+def test_economizer_runs():
+    refrigerant = RefrigerantLibrary('R290')
+    calc = CycleCalculator(refrigerant)
+    evap = 0.2 * 1e5
+    cond = 6.0 * 1e5
+    inter = 2.0 * 1e5
+    res = calc.calculate_cycle_with_economizer(evap, cond, inter, mass_flow=0.1)
+    assert 'performance' in res
+    assert 'flash_fraction' in res['performance']
+    assert 0.0 <= res['performance']['flash_fraction'] <= 1.0