From 616fb34ced7d180664330118f6e7ab96ef2a2fc8 Mon Sep 17 00:00:00 2001
From: radek_poleski <radek.poleski@gmail.com>
Date: Thu, 2 May 2024 07:51:00 +0200
Subject: [PATCH] more tests on q_source

---
 source/MulensModel/modelparameters.py         | 23 +++++++++++++++----
 .../MulensModel/tests/test_ModelParameters.py |  7 ++++++
 2 files changed, 26 insertions(+), 4 deletions(-)

diff --git a/source/MulensModel/modelparameters.py b/source/MulensModel/modelparameters.py
index 0266c632..bdc67673 100644
--- a/source/MulensModel/modelparameters.py
+++ b/source/MulensModel/modelparameters.py
@@ -480,13 +480,28 @@ def _divide_parameters(self, parameters):
                 parameters_2[key] = value
 
         if self.n_sources == 2 and self._type['xallarap']:
-            if parameters['q_source'] < 0.:
-                raise ValueError('q_source cannot be negative')
-            parameters_2['xi_semimajor_axis'] /= parameters['q_source']
-            parameters_2['xi_argument_of_latitude_reference'] += 180.
+            self._set_changed_parameters_2nd_source(parameters['q_source'],
+                                                    parameters_2)
 
         return (parameters_1, parameters_2)
 
+    def _set_changed_parameters_2nd_source(self, q_source, parameters_2):
+        """
+        For xallarap model with 2 sources, the orbit of the second source
+        must have 2 parameters changed.
+        Functions starts with tests of input
+        """
+        if q_source <= 0.:
+            raise ValueError('q_source cannot be negative')
+
+        check_keys = ['xi_semimajor_axis', 'xi_argument_of_latitude_reference']
+        for key in check_keys:
+            if key not in parameters_2:
+                raise KeyError('xallarap model with 2 sources requires ' + key)
+
+        parameters_2['xi_semimajor_axis'] /= q_source
+        parameters_2['xi_argument_of_latitude_reference'] += 180.
+
     def __repr__(self):
         """A nice way to represent a ModelParameters object as a string"""
         out = self._get_main_parameters_to_print()
diff --git a/source/MulensModel/tests/test_ModelParameters.py b/source/MulensModel/tests/test_ModelParameters.py
index 8cd77104..670b19a5 100644
--- a/source/MulensModel/tests/test_ModelParameters.py
+++ b/source/MulensModel/tests/test_ModelParameters.py
@@ -601,6 +601,13 @@ def test_no_q_source_but_with_rho_2(self):
         with self.assertRaises(KeyError):
             mm.ModelParameters(parameters)
 
+    def test_PSPL_and_q_source(self):
+        """
+        Make sure one cannot provide only PSPL parameters and q_source.
+        """
+        with self.assertRaises(KeyError):
+            mm.ModelParameters({'t_0': 1, 'u_0': 2, 't_E': 3, 'q_source': 1})
+
 
 def test_print_xallarap():
     """