fix: custom modifier / new parameter support and test

src/pyhf/pdf.py

@@ -357,7 +357,7 @@ def set_poi(self, name):
             >>> model.config.poi_name
             'mu'
         """
-        if name not in [x for x, _ in self.modifiers]:
+        if name not in self.parameters:
             raise exceptions.InvalidModel(
                 f"The parameter of interest '{name:s}' cannot be fit as it is not declared in the model specification."
             )

tests/test_custom_mods.py

@@ -0,0 +1,109 @@
+import pyhf
+import pyhf.exceptions as exceptions
+import pytest
+
+
+class custom_builder:
+    def __init__(self, pdfconfig):
+        self.config = pdfconfig
+        self.required_parsets = {
+            'k1': [
+                {
+                    'paramset_type': 'unconstrained',
+                    'n_parameters': 1,
+                    'is_constrained': False,
+                    'is_shared': True,
+                    'inits': (1.0,),
+                    'bounds': ((-5, 5),),
+                    'fixed': False,
+                }
+            ]
+        }
+        self.builder_data = {}
+
+    def append(self, key, channel, sample, thismod, defined_samp):
+        pass
+
+    def finalize(self):
+        return self.builder_data
+
+
+class custom_applicator:
+    op_code = 'multiplication'
+    name = 'customfunc'
+
+    def __init__(
+        self, modifiers=None, pdfconfig=None, builder_data=None, batch_size=None
+    ):
+        pass
+
+    def apply(self, pars):
+        raise NotImplementedError
+
+
+def test_custom_mods():
+    modifier_set = {custom_applicator.name: (custom_builder, custom_applicator)}
+    modifier_set.update(**pyhf.modifiers.histfactory_set)
+
+    model = pyhf.Model(
+        {
+            'channels': [
+                {
+                    'name': 'singlechannel',
+                    'samples': [
+                        {
+                            'name': 'signal',
+                            'data': [10] * 20,
+                            'modifiers': [
+                                {
+                                    'name': 'singlemod',
+                                    'type': 'customfunc',
+                                    'data': None,
+                                },
+                            ],
+                        },
+                        {'name': 'background', 'data': [300] * 20, 'modifiers': []},
+                    ],
+                }
+            ]
+        },
+        modifier_set=modifier_set,
+        poi_name='k1',
+        validate=False,
+    )
+    assert model
+    assert 'k1' in model.config.parameters
+
+
+def test_missing_poi():
+    modifier_set = {custom_applicator.name: (custom_builder, custom_applicator)}
+    modifier_set.update(**pyhf.modifiers.histfactory_set)
+
+    with pytest.raises(exceptions.InvalidModel):
+        model = pyhf.Model(
+            {
+                'channels': [
+                    {
+                        'name': 'singlechannel',
+                        'samples': [
+                            {
+                                'name': 'signal',
+                                'data': [10] * 20,
+                                'modifiers': [
+                                    {
+                                        'name': 'singlemod',
+                                        'type': 'customfunc',
+                                        'data': None,
+                                    },
+                                ],
+                            },
+                            {'name': 'background', 'data': [300] * 20, 'modifiers': []},
+                        ],
+                    }
+                ]
+            },
+            modifier_set=modifier_set,
+            poi_name='non_existent_poi',
+            validate=False,
+        )
+        assert model