Add integration test

tests/integration/fitting/test_fitting_with_diffusion_model.py

@@ -0,0 +1,152 @@
+# SPDX-FileCopyrightText: 2026 EasyScience contributors <https://github.com/easyscience>
+# SPDX-License-Identifier: BSD-3-Clause
+
+import numpy as np
+import pooch
+
+from easydynamics.analysis.analysis import Analysis
+from easydynamics.experiment import Experiment
+from easydynamics.sample_model import ComponentCollection
+from easydynamics.sample_model import DeltaFunction
+from easydynamics.sample_model import Gaussian
+from easydynamics.sample_model import Lorentzian
+from easydynamics.sample_model import Polynomial
+from easydynamics.sample_model.background_model import BackgroundModel
+from easydynamics.sample_model.diffusion_model.brownian_translational_diffusion import (
+    BrownianTranslationalDiffusion,
+)
+from easydynamics.sample_model.instrument_model import InstrumentModel
+from easydynamics.sample_model.resolution_model import ResolutionModel
+from easydynamics.sample_model.sample_model import SampleModel
+
+
+class TestFittingWithDiffusionModel:
+    def test_fitting_with_diffusion_model(self):
+        # Load the vanadium data
+        vanadium_experiment = Experiment('Vanadium')
+
+        file_path = pooch.retrieve(
+            url='https://github.com/easyscience/dynamics-lib/raw/refs/heads/master/docs/docs/tutorials/data/vanadium_data_example.h5',
+            known_hash='16cc1b327c303feeb88fb9dda5390dc4880b62396b1793f98c6fef0b27c7b873',
+        )
+
+        vanadium_experiment.load_hdf5(filename=file_path)
+
+        delta_function = DeltaFunction(display_name='DeltaFunction', area=1)
+        sample_model = SampleModel(components=delta_function)
+
+        resolution_components = ComponentCollection()
+        res_gauss = Gaussian(width=0.1, area=1, display_name='Res. Gauss')
+        res_gauss.area.fixed = True
+        resolution_components.append_component(res_gauss)
+        resolution_model = ResolutionModel(components=resolution_components)
+
+        background_model = BackgroundModel(components=Polynomial(coefficients=[0.001]))
+
+        instrument_model = InstrumentModel(
+            resolution_model=resolution_model,
+            background_model=background_model,
+        )
+
+        vanadium_analysis = Analysis(
+            display_name='Vanadium Full Analysis',
+            experiment=vanadium_experiment,
+            sample_model=sample_model,
+            instrument_model=instrument_model,
+        )
+
+        fit_result_independent_single_Q = vanadium_analysis.fit(
+            fit_method='independent', Q_index=5
+        )
+
+        assert fit_result_independent_single_Q.success
+        assert fit_result_independent_single_Q.chi2 < 75.0
+        assert fit_result_independent_single_Q.reduced_chi < 0.4
+
+        diffusion_experiment = Experiment('Diffusion')
+
+        file_path = pooch.retrieve(
+            url='https://github.com/easyscience/dynamics-lib/raw/refs/heads/master/docs/docs/tutorials/data/diffusion_data_example.h5',
+            known_hash='5fe846b19aacbda8b8b936eb2e5310d025dc56c25b0b353521e7d6b921f229ab',
+        )
+
+        diffusion_experiment.load_hdf5(filename=file_path)
+
+        delta_function = DeltaFunction(display_name='DeltaFunction', area=0.2)
+        lorentzian = Lorentzian(display_name='Lorentzian', area=0.5, width=0.3)
+        component_collection = ComponentCollection(
+            components=[delta_function, lorentzian],
+        )
+
+        sample_model = SampleModel(
+            components=component_collection,
+        )
+
+        background_model = BackgroundModel(components=Polynomial(coefficients=[0.001]))
+
+        instrument_model = InstrumentModel(
+            background_model=background_model,
+            resolution_model=vanadium_analysis.instrument_model.resolution_model,
+        )
+        instrument_model.resolution_model.fix_all_parameters()
+
+        diffusion_analysis = Analysis(
+            display_name='Diffusion Analysis',
+            experiment=diffusion_experiment,
+            sample_model=sample_model,
+            instrument_model=instrument_model,
+        )
+
+        fit_result = diffusion_analysis.fit(fit_method='independent')
+
+        assert fit_result[0].success
+        assert fit_result[0].chi2 < 43.0
+        assert fit_result[0].reduced_chi < 0.3
+
+        ###############
+        # Diffusion model
+        ###############
+
+        delta_function = DeltaFunction(display_name='DeltaFunction', area=0.2)
+        component_collection = ComponentCollection(
+            components=[delta_function],
+        )
+        diffusion_model = BrownianTranslationalDiffusion(
+            display_name='Brownian Translational Diffusion',
+            diffusion_coefficient=2.4e-9,
+            scale=0.5,
+        )
+
+        sample_model = SampleModel(
+            components=component_collection,
+            diffusion_models=diffusion_model,
+        )
+
+        background_model = BackgroundModel(components=Polynomial(coefficients=[0.001]))
+
+        instrument_model = InstrumentModel(
+            background_model=background_model,
+            resolution_model=vanadium_analysis.instrument_model.resolution_model,
+        )
+
+        diffusion_model_analysis = Analysis(
+            display_name='Diffusion Full Analysis',
+            experiment=diffusion_experiment,
+            sample_model=sample_model,
+            instrument_model=instrument_model,
+        )
+
+        diffusion_model_analysis.instrument_model.resolution_model.fix_all_parameters()
+
+        fit_result = diffusion_model_analysis.fit(fit_method='simultaneous')
+
+        assert fit_result[0].success
+        assert fit_result[0].chi2 < 56.0
+        assert fit_result[0].reduced_chi < 0.4
+
+        pars = diffusion_model.get_all_parameters()
+
+        tol = 10 * pars[0].error
+        assert np.isclose(pars[0].value, 1.1258025622851164e-08, atol=tol)
+        tol = 10 * pars[1].error
+        assert np.isclose(pars[1].value, 0.6937774083152299, atol=tol)