diff --git a/.github/workflows/tests-on-pr.yml b/.github/workflows/tests-on-pr.yml
index f9b4d90..dfdbc77 100644
--- a/.github/workflows/tests-on-pr.yml
+++ b/.github/workflows/tests-on-pr.yml
@@ -36,8 +36,8 @@ jobs:
       - name: Install diffpy.srreal and requirements
         run: |
           conda install --file requirements/test.txt
-          conda install --file requirements/conda.txt
+          conda install boost numpy libdiffpy setuptools diffpy.structure periodictable gsl
           python -m pip install . --no-deps
 
       - name: Validate diffpy.pdfgui
-        run: python -m diffpy.srreal.tests.run
+        run: pytest tests
diff --git a/src/diffpy/srreal/tests/__init__.py b/src/diffpy/srreal/tests/__init__.py
deleted file mode 100644
index c4e942b..0000000
--- a/src/diffpy/srreal/tests/__init__.py
+++ /dev/null
@@ -1,85 +0,0 @@
-#!/usr/bin/env python
-##############################################################################
-#
-# diffpy.srreal     by DANSE Diffraction group
-#                   Simon J. L. Billinge
-#                   (c) 2012 The Trustees of Columbia University
-#                   in the City of New York.  All rights reserved.
-#
-# File coded by:    Pavol Juhas
-#
-# See AUTHORS.txt for a list of people who contributed.
-# See LICENSE_DANSE.txt for license information.
-#
-##############################################################################
-"""Unit tests for diffpy.srreal."""
-
-import logging
-import unittest
-
-# create logger instance for the tests subpackage
-logging.basicConfig()
-logger = logging.getLogger(__name__)
-del logging
-
-
-def testsuite(pattern=""):
-    """Create a unit tests suite for diffpy.srreal package.
-
-    Parameters
-    ----------
-    pattern : str, optional
-        Regular expression pattern for selecting test cases.
-        Select all tests when empty.  Ignore the pattern when
-        any of unit test modules fails to import.
-
-    Returns
-    -------
-    suite : `unittest.TestSuite`
-        The TestSuite object containing the matching tests.
-    """
-    import re
-    from itertools import chain
-    from os.path import dirname
-
-    from pkg_resources import resource_filename
-
-    loader = unittest.defaultTestLoader
-    thisdir = resource_filename(__name__, "")
-    depth = __name__.count(".") + 1
-    topdir = thisdir
-    for i in range(depth):
-        topdir = dirname(topdir)
-    suite_all = loader.discover(thisdir, top_level_dir=topdir)
-    # always filter the suite by pattern to test-cover the selection code.
-    suite = unittest.TestSuite()
-    rx = re.compile(pattern)
-    tsuites = list(chain.from_iterable(suite_all))
-    tsok = all(isinstance(ts, unittest.TestSuite) for ts in tsuites)
-    if not tsok:  # pragma: no cover
-        return suite_all
-    tcases = chain.from_iterable(tsuites)
-    for tc in tcases:
-        tcwords = tc.id().split(".")
-        shortname = ".".join(tcwords[-3:])
-        if rx.search(shortname):
-            suite.addTest(tc)
-    # verify all tests are found for an empty pattern.
-    assert pattern or suite_all.countTestCases() == suite.countTestCases()
-    return suite
-
-
-def test():
-    """Execute all unit tests for the diffpy.srreal package.
-
-    Returns
-    -------
-    result : `unittest.TestResult`
-    """
-    suite = testsuite()
-    runner = unittest.TextTestRunner()
-    result = runner.run(suite)
-    return result
-
-
-# End of file
diff --git a/src/diffpy/srreal/tests/debug.py b/src/diffpy/srreal/tests/debug.py
deleted file mode 100644
index 47197f9..0000000
--- a/src/diffpy/srreal/tests/debug.py
+++ /dev/null
@@ -1,33 +0,0 @@
-#!/usr/bin/env python
-##############################################################################
-#
-# diffpy.srreal     Complex Modeling Initiative
-#                   (c) 2016 Brookhaven Science Associates,
-#                   Brookhaven National Laboratory.
-#                   All rights reserved.
-#
-# File coded by:    Pavol Juhas
-#
-# See AUTHORS.txt for a list of people who contributed.
-# See LICENSE.txt for license information.
-#
-##############################################################################
-"""Convenience module for debugging the unit tests using.
-
-python -m diffpy.srreal.tests.debug
-
-Exceptions raised by failed tests or other errors are not caught.
-"""
-
-
-if __name__ == "__main__":
-    import sys
-
-    from diffpy.srreal.tests import testsuite
-
-    pattern = sys.argv[1] if len(sys.argv) > 1 else ""
-    suite = testsuite(pattern)
-    suite.debug()
-
-
-# End of file
diff --git a/src/diffpy/srreal/tests/run.py b/src/diffpy/srreal/tests/run.py
deleted file mode 100644
index 9d10705..0000000
--- a/src/diffpy/srreal/tests/run.py
+++ /dev/null
@@ -1,37 +0,0 @@
-#!/usr/bin/env python
-##############################################################################
-#
-# diffpy.srreal     by DANSE Diffraction group
-#                   Simon J. L. Billinge
-#                   (c) 2010 The Trustees of Columbia University
-#                   in the City of New York.  All rights reserved.
-#
-# File coded by:    Pavol Juhas
-#
-# See AUTHORS.txt for a list of people who contributed.
-# See LICENSE_DANSE.txt for license information.
-#
-##############################################################################
-"""Convenience module for executing all unit tests with.
-
-python -m diffpy.srreal.tests.run
-"""
-
-
-if __name__ == "__main__":
-    import sys
-
-    # show warnings by default
-    if not sys.warnoptions:
-        import os
-        import warnings
-
-        warnings.simplefilter("default")
-        # also affect subprocesses
-        os.environ["PYTHONWARNINGS"] = "default"
-    from diffpy.srreal.tests import test
-
-    # produce zero exit code for a successful test
-    sys.exit(not test().wasSuccessful())
-
-# End of file
diff --git a/tests/conftest.py b/tests/conftest.py
new file mode 100644
index 0000000..ac3c222
--- /dev/null
+++ b/tests/conftest.py
@@ -0,0 +1,75 @@
+import json
+import logging
+from pathlib import Path
+
+import pytest
+
+from diffpy.srreal.structureconverters import convertObjCrystCrystal
+
+
+@pytest.fixture
+def user_filesystem(tmp_path):
+    base_dir = Path(tmp_path)
+    home_dir = base_dir / "home_dir"
+    home_dir.mkdir(parents=True, exist_ok=True)
+    cwd_dir = base_dir / "cwd_dir"
+    cwd_dir.mkdir(parents=True, exist_ok=True)
+
+    home_config_data = {"username": "home_username", "email": "home@email.com"}
+    with open(home_dir / "diffpyconfig.json", "w") as f:
+        json.dump(home_config_data, f)
+
+    yield tmp_path
+
+
+# Resolve availability of optional packages.
+
+# pyobjcryst
+
+
+@pytest.fixture(scope="session")
+def _msg_nopyobjcryst():
+    return "No module named 'pyobjcryst'"
+
+
+@pytest.fixture(scope="session")
+def has_pyobjcryst():
+    try:
+        import pyobjcryst.crystal
+
+        convertObjCrystCrystal(pyobjcryst.crystal.Crystal())
+        has_pyobjcryst = True
+    except ImportError:
+        has_pyobjcryst = False
+        logging.warning("Cannot import pyobjcryst, pyobjcryst tests skipped.")
+        print("Cannot import pyobjcryst, pyobjcryst tests skipped.")
+    except TypeError:
+        has_pyobjcryst = False
+        logging.warning("Compiled without ObjCryst, pyobjcryst tests skipped.")
+        print("Compiled without ObjCryst, pyobjcryst tests skipped.")
+
+    return has_pyobjcryst
+
+
+# periodictable
+
+
+@pytest.fixture(scope="session")
+def _msg_noperiodictable():
+    return "No module named 'periodictable'"
+
+
+@pytest.fixture(scope="session")
+def has_periodictable():
+    try:
+        import periodictable
+
+        has_periodictable = True
+
+        # silence the pyflakes syntax checker
+        del periodictable
+    except ImportError:
+        has_periodictable = False
+        logging.warning("Cannot import periodictable, periodictable tests skipped.")
+
+    return has_periodictable
diff --git a/src/diffpy/srreal/tests/testatomradiitable.py b/tests/test_atomradiitable.py
similarity index 96%
rename from src/diffpy/srreal/tests/testatomradiitable.py
rename to tests/test_atomradiitable.py
index f5c2265..158a6f4 100644
--- a/src/diffpy/srreal/tests/testatomradiitable.py
+++ b/tests/test_atomradiitable.py
@@ -6,14 +6,14 @@
 import pickle
 import unittest
 
+import pytest
+
 from diffpy.srreal.atomradiitable import AtomRadiiTable, ConstantRadiiTable, CovalentRadiiTable
-from diffpy.srreal.tests.testutils import _msg_noperiodictable, has_periodictable
 
 # ----------------------------------------------------------------------------
 
 
 class TestAtomRadiiTable(unittest.TestCase):
-
     def setUp(self):
         self.rtb = AtomRadiiTable()
         self.ctb = ConstantRadiiTable()
@@ -103,9 +103,13 @@ def test_toString(self):
 # ----------------------------------------------------------------------------
 
 
-@unittest.skipUnless(has_periodictable, _msg_noperiodictable)
 class TestCovalentRadiiTable(unittest.TestCase):
 
+    @pytest.fixture(autouse=True)
+    def _check_periodictable(self, has_periodictable, _msg_noperiodictable):
+        if not has_periodictable:
+            pytest.skip(_msg_noperiodictable)
+
     def setUp(self):
         self.rtb = CovalentRadiiTable()
         return
diff --git a/src/diffpy/srreal/tests/testattributes.py b/tests/test_attributes.py
similarity index 100%
rename from src/diffpy/srreal/tests/testattributes.py
rename to tests/test_attributes.py
diff --git a/src/diffpy/srreal/tests/testbondcalculator.py b/tests/test_bondcalculator.py
similarity index 97%
rename from src/diffpy/srreal/tests/testbondcalculator.py
rename to tests/test_bondcalculator.py
index cbbe609..cd69fe5 100644
--- a/src/diffpy/srreal/tests/testbondcalculator.py
+++ b/tests/test_bondcalculator.py
@@ -7,15 +7,10 @@
 import unittest
 
 import numpy
+import pytest
+from testutils import loadDiffPyStructure, loadObjCrystCrystal, pickle_with_attr
 
 from diffpy.srreal.bondcalculator import BondCalculator
-from diffpy.srreal.tests.testutils import (
-    _msg_nopyobjcryst,
-    has_pyobjcryst,
-    loadDiffPyStructure,
-    loadObjCrystCrystal,
-    pickle_with_attr,
-)
 
 # ----------------------------------------------------------------------------
 
@@ -81,7 +76,7 @@ def test_pickling(self):
 
     def test_pickling_derived_structure(self):
         """Check pickling of BondCalculator with DerivedStructureAdapter."""
-        from diffpy.srreal.tests.testutils import DerivedStructureAdapter
+        from testutils import DerivedStructureAdapter
 
         bdc = self.bdc
         stru0 = DerivedStructureAdapter()
@@ -249,9 +244,13 @@ def test_setTypeMask(self):
 # ----------------------------------------------------------------------------
 
 
-@unittest.skipUnless(has_pyobjcryst, _msg_nopyobjcryst)
 class TestBondCalculatorObjCryst(unittest.TestCase):
 
+    @pytest.fixture(autouse=True)
+    def _check_periodictable(self, has_pyobjcryst, _msg_nopyobjcryst):
+        if not has_pyobjcryst:
+            pytest.skip(_msg_nopyobjcryst)
+
     def setUp(self):
         self.bdc = BondCalculator()
         if not hasattr(self, "rutile"):
diff --git a/src/diffpy/srreal/tests/testbvscalculator.py b/tests/test_bvscalculator.py
similarity index 97%
rename from src/diffpy/srreal/tests/testbvscalculator.py
rename to tests/test_bvscalculator.py
index aceac21..c2f3838 100644
--- a/src/diffpy/srreal/tests/testbvscalculator.py
+++ b/tests/test_bvscalculator.py
@@ -6,8 +6,9 @@
 import pickle
 import unittest
 
+from testutils import loadDiffPyStructure, pickle_with_attr
+
 from diffpy.srreal.bvscalculator import BVSCalculator
-from diffpy.srreal.tests.testutils import loadDiffPyStructure, pickle_with_attr
 
 
 ##############################################################################
@@ -139,7 +140,7 @@ def test_table_pickling(self):
 
     def test_pickling_derived_structure(self):
         """Check pickling of BVSCalculator with DerivedStructureAdapter."""
-        from diffpy.srreal.tests.testutils import DerivedStructureAdapter
+        from testutils import DerivedStructureAdapter
 
         bvc = self.bvc
         stru0 = DerivedStructureAdapter()
diff --git a/src/diffpy/srreal/tests/testdebyepdfcalculator.py b/tests/test_debyepdfcalculator.py
similarity index 97%
rename from src/diffpy/srreal/tests/testdebyepdfcalculator.py
rename to tests/test_debyepdfcalculator.py
index fd8c07d..693a7ab 100644
--- a/src/diffpy/srreal/tests/testdebyepdfcalculator.py
+++ b/tests/test_debyepdfcalculator.py
@@ -7,10 +7,9 @@
 import unittest
 
 import numpy
+from testutils import _maxNormDiff, loadDiffPyStructure, pickle_with_attr
 
 from diffpy.srreal.pdfcalculator import DebyePDFCalculator, PDFCalculator
-from diffpy.srreal.tests.testpdfcalculator import _maxNormDiff
-from diffpy.srreal.tests.testutils import loadDiffPyStructure, pickle_with_attr
 
 
 ##############################################################################
@@ -189,7 +188,7 @@ def test_mask_pickling(self):
     def test_pickling_derived_structure(self):
         """Check pickling of DebyePDFCalculator with
         DerivedStructureAdapter."""
-        from diffpy.srreal.tests.testutils import DerivedStructureAdapter
+        from testutils import DerivedStructureAdapter
 
         dpdfc = self.dpdfc
         stru0 = DerivedStructureAdapter()
diff --git a/src/diffpy/srreal/tests/testoverlapcalculator.py b/tests/test_overlapcalculator.py
similarity index 98%
rename from src/diffpy/srreal/tests/testoverlapcalculator.py
rename to tests/test_overlapcalculator.py
index aabda0e..5a7a204 100644
--- a/src/diffpy/srreal/tests/testoverlapcalculator.py
+++ b/tests/test_overlapcalculator.py
@@ -8,16 +8,11 @@
 import unittest
 
 import numpy
+import pytest
+from testutils import loadDiffPyStructure, loadObjCrystCrystal, pickle_with_attr
 
 from diffpy.srreal.atomradiitable import CovalentRadiiTable
 from diffpy.srreal.overlapcalculator import OverlapCalculator
-from diffpy.srreal.tests.testutils import (
-    _msg_nopyobjcryst,
-    has_pyobjcryst,
-    loadDiffPyStructure,
-    loadObjCrystCrystal,
-    pickle_with_attr,
-)
 
 # ----------------------------------------------------------------------------
 
@@ -117,7 +112,7 @@ def test_pickling_artb(self):
 
     def test_pickling_derived_structure(self):
         """Check pickling of OverlapCalculator with DerivedStructureAdapter."""
-        from diffpy.srreal.tests.testutils import DerivedStructureAdapter
+        from testutils import DerivedStructureAdapter
 
         olc = self.olc
         stru0 = DerivedStructureAdapter()
@@ -332,9 +327,13 @@ def test_neighborhoods(self):
 # ----------------------------------------------------------------------------
 
 
-@unittest.skipUnless(has_pyobjcryst, _msg_nopyobjcryst)
 class TestOverlapCalculatorObjCryst(unittest.TestCase):
 
+    @pytest.fixture(autouse=True)
+    def _check_periodictable(self, has_pyobjcryst, _msg_nopyobjcryst):
+        if not has_pyobjcryst:
+            pytest.skip(_msg_nopyobjcryst)
+
     def setUp(self):
         self.olc = OverlapCalculator()
         if not hasattr(self, "rutile"):
diff --git a/src/diffpy/srreal/tests/testpairquantity.py b/tests/test_pairquantity.py
similarity index 98%
rename from src/diffpy/srreal/tests/testpairquantity.py
rename to tests/test_pairquantity.py
index c07da95..01e3bd9 100644
--- a/src/diffpy/srreal/tests/testpairquantity.py
+++ b/tests/test_pairquantity.py
@@ -6,11 +6,11 @@
 import unittest
 
 import numpy
+from testutils import mod_structure
 
 from diffpy.srreal.pairquantity import PairQuantity
 from diffpy.srreal.pdfcalculator import PDFCalculator
 from diffpy.srreal.srreal_ext import BasePairQuantity
-from diffpy.srreal.tests.testutils import mod_structure
 
 # ----------------------------------------------------------------------------
 
@@ -169,7 +169,7 @@ def eval_as(evtp, pq, stru):
 
     def test_pickling(self):
         """Check pickling and unpickling of PairQuantity."""
-        from diffpy.srreal.tests.testutils import DerivedStructureAdapter
+        from testutils import DerivedStructureAdapter
 
         stru0 = DerivedStructureAdapter()
         self.pq.setStructure(stru0)
diff --git a/src/diffpy/srreal/tests/testparallel.py b/tests/test_parallel.py
similarity index 98%
rename from src/diffpy/srreal/tests/testparallel.py
rename to tests/test_parallel.py
index e6ae9c1..3bc524c 100644
--- a/src/diffpy/srreal/tests/testparallel.py
+++ b/tests/test_parallel.py
@@ -7,9 +7,9 @@
 import unittest
 
 import numpy
+from testutils import loadDiffPyStructure
 
 from diffpy.srreal.parallel import createParallelCalculator
-from diffpy.srreal.tests.testutils import loadDiffPyStructure
 
 
 ##############################################################################
diff --git a/src/diffpy/srreal/tests/testpdfbaseline.py b/tests/test_pdfbaseline.py
similarity index 99%
rename from src/diffpy/srreal/tests/testpdfbaseline.py
rename to tests/test_pdfbaseline.py
index 152119e..20535ce 100644
--- a/src/diffpy/srreal/tests/testpdfbaseline.py
+++ b/tests/test_pdfbaseline.py
@@ -7,10 +7,10 @@
 import unittest
 
 import numpy
+from testutils import pickle_with_attr
 
 from diffpy.srreal.pdfbaseline import LinearBaseline, PDFBaseline, ZeroBaseline, makePDFBaseline
 from diffpy.srreal.pdfcalculator import PDFCalculator
-from diffpy.srreal.tests.testutils import pickle_with_attr
 
 # ----------------------------------------------------------------------------
 
diff --git a/src/diffpy/srreal/tests/testpdfcalcobjcryst.py b/tests/test_pdfcalcobjcryst.py
similarity index 92%
rename from src/diffpy/srreal/tests/testpdfcalcobjcryst.py
rename to tests/test_pdfcalcobjcryst.py
index 01ef21b..3fd4d4c 100644
--- a/src/diffpy/srreal/tests/testpdfcalcobjcryst.py
+++ b/tests/test_pdfcalcobjcryst.py
@@ -7,10 +7,10 @@
 import unittest
 
 import numpy
+import pytest
+from testutils import _maxNormDiff, datafile, loadObjCrystCrystal
 
 from diffpy.srreal.pdfcalculator import PDFCalculator
-from diffpy.srreal.tests.testpdfcalculator import _maxNormDiff
-from diffpy.srreal.tests.testutils import _msg_nopyobjcryst, datafile, has_pyobjcryst, loadObjCrystCrystal
 
 # helper functions
 
@@ -59,9 +59,13 @@ def _makePDFCalculator(crst, cfgdict):
 # ----------------------------------------------------------------------------
 
 
-@unittest.skipUnless(has_pyobjcryst, _msg_nopyobjcryst)
 class TestPDFCalcObjcryst(unittest.TestCase):
 
+    @pytest.fixture(autouse=True)
+    def _check_periodictable(self, has_pyobjcryst, _msg_nopyobjcryst):
+        if not has_pyobjcryst:
+            pytest.skip(_msg_nopyobjcryst)
+
     def _comparePDFs(self, nickname, pdfbasename, cifbasename):
         def setself(**kwtoset):
             for n, v in kwtoset.items():
diff --git a/src/diffpy/srreal/tests/testpdfcalculator.py b/tests/test_pdfcalculator.py
similarity index 96%
rename from src/diffpy/srreal/tests/testpdfcalculator.py
rename to tests/test_pdfcalculator.py
index 5b79003..ef45a6b 100644
--- a/src/diffpy/srreal/tests/testpdfcalculator.py
+++ b/tests/test_pdfcalculator.py
@@ -7,22 +7,13 @@
 import unittest
 
 import numpy
+from testutils import _maxNormDiff, datafile, loadDiffPyStructure, pickle_with_attr
 
 from diffpy.srreal.pdfcalculator import PDFCalculator, fftftog, fftgtof
-from diffpy.srreal.tests.testutils import datafile, loadDiffPyStructure, pickle_with_attr
 
 # helper functions
 
 
-def _maxNormDiff(yobs, ycalc):
-    """Returned maximum difference normalized by RMS of the yobs."""
-    yobsa = numpy.array(yobs)
-    obsmax = numpy.max(numpy.fabs(yobsa)) or 1
-    ynmdiff = (yobsa - ycalc) / obsmax
-    rv = max(numpy.fabs(ynmdiff))
-    return rv
-
-
 # ----------------------------------------------------------------------------
 
 
@@ -274,7 +265,7 @@ def test_mask_pickling(self):
 
     def test_pickling_derived_structure(self):
         """Check pickling of PDFCalculator with DerivedStructureAdapter."""
-        from diffpy.srreal.tests.testutils import DerivedStructureAdapter
+        from testutils import DerivedStructureAdapter
 
         pdfc = self.pdfcalc
         stru0 = DerivedStructureAdapter()
diff --git a/src/diffpy/srreal/tests/testpdfenvelope.py b/tests/test_pdfenvelope.py
similarity index 99%
rename from src/diffpy/srreal/tests/testpdfenvelope.py
rename to tests/test_pdfenvelope.py
index cf84055..7ea75f4 100644
--- a/src/diffpy/srreal/tests/testpdfenvelope.py
+++ b/tests/test_pdfenvelope.py
@@ -7,6 +7,7 @@
 import unittest
 
 import numpy
+from testutils import pickle_with_attr
 
 from diffpy.srreal.pdfcalculator import DebyePDFCalculator, PDFCalculator
 from diffpy.srreal.pdfenvelope import (
@@ -17,7 +18,6 @@
     StepCutEnvelope,
     makePDFEnvelope,
 )
-from diffpy.srreal.tests.testutils import pickle_with_attr
 
 # ----------------------------------------------------------------------------
 
diff --git a/src/diffpy/srreal/tests/testpeakprofile.py b/tests/test_peakprofile.py
similarity index 98%
rename from src/diffpy/srreal/tests/testpeakprofile.py
rename to tests/test_peakprofile.py
index 56e3943..9b739c1 100644
--- a/src/diffpy/srreal/tests/testpeakprofile.py
+++ b/tests/test_peakprofile.py
@@ -7,10 +7,10 @@
 import unittest
 
 import numpy
+from testutils import mod_structure, pickle_with_attr
 
 from diffpy.srreal.pdfcalculator import PDFCalculator
 from diffpy.srreal.peakprofile import PeakProfile
-from diffpy.srreal.tests.testutils import mod_structure, pickle_with_attr
 
 # ----------------------------------------------------------------------------
 
diff --git a/src/diffpy/srreal/tests/testpeakwidthmodel.py b/tests/test_peakwidthmodel.py
similarity index 99%
rename from src/diffpy/srreal/tests/testpeakwidthmodel.py
rename to tests/test_peakwidthmodel.py
index 0ba053f..6c83cd1 100644
--- a/src/diffpy/srreal/tests/testpeakwidthmodel.py
+++ b/tests/test_peakwidthmodel.py
@@ -7,10 +7,11 @@
 import pickle
 import unittest
 
+from testutils import loadDiffPyStructure
+
 from diffpy.srreal.pdfcalculator import DebyePDFCalculator, PDFCalculator
 from diffpy.srreal.peakwidthmodel import DebyeWallerPeakWidth, JeongPeakWidth, PeakWidthModel
 from diffpy.srreal.structureadapter import createStructureAdapter
-from diffpy.srreal.tests.testutils import loadDiffPyStructure
 
 # ----------------------------------------------------------------------------
 
diff --git a/src/diffpy/srreal/tests/testscatteringfactortable.py b/tests/test_scatteringfactortable.py
similarity index 99%
rename from src/diffpy/srreal/tests/testscatteringfactortable.py
rename to tests/test_scatteringfactortable.py
index e4c95be..3d327ae 100644
--- a/src/diffpy/srreal/tests/testscatteringfactortable.py
+++ b/tests/test_scatteringfactortable.py
@@ -7,6 +7,7 @@
 import unittest
 
 import numpy
+from testutils import pickle_with_attr
 
 from diffpy.srreal.pdfcalculator import DebyePDFCalculator, PDFCalculator
 from diffpy.srreal.scatteringfactortable import (
@@ -16,7 +17,6 @@
     SFTNeutron,
     SFTXray,
 )
-from diffpy.srreal.tests.testutils import pickle_with_attr
 
 # ----------------------------------------------------------------------------
 
diff --git a/src/diffpy/srreal/tests/testsfaverage.py b/tests/test_sfaverage.py
similarity index 93%
rename from src/diffpy/srreal/tests/testsfaverage.py
rename to tests/test_sfaverage.py
index 6efaa98..87dd9a1 100644
--- a/src/diffpy/srreal/tests/testsfaverage.py
+++ b/tests/test_sfaverage.py
@@ -6,15 +6,11 @@
 import unittest
 
 import numpy
+import pytest
+from testutils import loadDiffPyStructure, loadObjCrystCrystal
 
 from diffpy.srreal.scatteringfactortable import ScatteringFactorTable
 from diffpy.srreal.sfaverage import SFAverage
-from diffpy.srreal.tests.testutils import (
-    _msg_nopyobjcryst,
-    has_pyobjcryst,
-    loadDiffPyStructure,
-    loadObjCrystCrystal,
-)
 
 # ----------------------------------------------------------------------------
 
@@ -78,9 +74,13 @@ def test_fromComposition(self):
 # ----------------------------------------------------------------------------
 
 
-@unittest.skipUnless(has_pyobjcryst, _msg_nopyobjcryst)
 class TestSFAverageObjCryst(unittest.TestCase):
 
+    @pytest.fixture(autouse=True)
+    def _check_periodictable(self, has_pyobjcryst, _msg_nopyobjcryst):
+        if not has_pyobjcryst:
+            pytest.skip(_msg_nopyobjcryst)
+
     def setUp(self):
         self.sftx = ScatteringFactorTable.createByType("X")
         return
diff --git a/src/diffpy/srreal/tests/teststructureadapter.py b/tests/test_structureadapter.py
similarity index 97%
rename from src/diffpy/srreal/tests/teststructureadapter.py
rename to tests/test_structureadapter.py
index 55a3604..697c355 100644
--- a/src/diffpy/srreal/tests/teststructureadapter.py
+++ b/tests/test_structureadapter.py
@@ -7,8 +7,17 @@
 import unittest
 
 import numpy
+import pytest
+from testutils import (
+    DerivedAtomicStructureAdapter,
+    DerivedCrystalStructureAdapter,
+    DerivedPeriodicStructureAdapter,
+    DerivedStructureAdapter,
+    loadCrystalStructureAdapter,
+    loadDiffPyStructure,
+    loadObjCrystCrystal,
+)
 
-import diffpy.srreal.tests.testutils as testutils
 from diffpy.srreal.pdfcalculator import PDFCalculator
 from diffpy.srreal.structureadapter import (
     Atom,
@@ -20,13 +29,6 @@
     nometa,
     nosymmetry,
 )
-from diffpy.srreal.tests.testutils import (
-    _msg_nopyobjcryst,
-    has_pyobjcryst,
-    loadCrystalStructureAdapter,
-    loadDiffPyStructure,
-    loadObjCrystCrystal,
-)
 
 # ----------------------------------------------------------------------------
 
@@ -110,7 +112,7 @@ def test_pickle_nonwrapped(self):
 class TestDerivedAdapter(unittest.TestCase):
     "Check functionality in a Python-derived StructureAdapter class."
 
-    DerivedCls = testutils.DerivedStructureAdapter
+    DerivedCls = DerivedStructureAdapter
 
     def setUp(self):
         self.adpt = self.DerivedCls()
@@ -145,15 +147,15 @@ def test_pickling(self):
 
 
 class TestDerivedAtomicAdapter(TestDerivedAdapter):
-    DerivedCls = testutils.DerivedAtomicStructureAdapter
+    DerivedCls = DerivedAtomicStructureAdapter
 
 
 class TestDerivedPeriodicAdapter(TestDerivedAdapter):
-    DerivedCls = testutils.DerivedPeriodicStructureAdapter
+    DerivedCls = DerivedPeriodicStructureAdapter
 
 
 class TestDerivedCrystalAdapter(TestDerivedAdapter):
-    DerivedCls = testutils.DerivedCrystalStructureAdapter
+    DerivedCls = DerivedCrystalStructureAdapter
 
 
 # ----------------------------------------------------------------------------
@@ -268,9 +270,13 @@ def test_nosymmetry_pickling(self):
 # ----------------------------------------------------------------------------
 
 
-@unittest.skipUnless(has_pyobjcryst, _msg_nopyobjcryst)
 class TestPyObjCrystAdapter(unittest.TestCase):
 
+    @pytest.fixture(autouse=True)
+    def _check_periodictable(self, has_pyobjcryst, _msg_nopyobjcryst):
+        if not has_pyobjcryst:
+            pytest.skip(_msg_nopyobjcryst)
+
     def setUp(self):
         rutile_crystal = loadObjCrystCrystal("TiO2_rutile-fit.cif")
         self.rutile = createStructureAdapter(rutile_crystal)
@@ -408,7 +414,7 @@ def test_getEquivalentAtoms(self):
 
 
 class TestDerivedStructureAdapter(IndexRangeTests, TestCase):
-    AdptClass = testutils.DerivedStructureAdapter
+    AdptClass = DerivedStructureAdapter
 
     def setUp(self):
         IndexRangeTests.setUp(self)
diff --git a/tests/test_version.py b/tests/test_version.py
new file mode 100644
index 0000000..d50b30d
--- /dev/null
+++ b/tests/test_version.py
@@ -0,0 +1,10 @@
+"""Unit tests for __version__.py."""
+
+import diffpy.srreal
+
+
+def test_package_version():
+    """Ensure the package version is defined and not set to the initial
+    placeholder."""
+    assert hasattr(diffpy.srreal, "__version__")
+    assert diffpy.srreal.__version__ != "0.0.0"
diff --git a/src/diffpy/srreal/tests/testdata/C60bucky.stru b/tests/testdata/C60bucky.stru
similarity index 100%
rename from src/diffpy/srreal/tests/testdata/C60bucky.stru
rename to tests/testdata/C60bucky.stru
diff --git a/src/diffpy/srreal/tests/testdata/CdSe_cadmoselite.cif b/tests/testdata/CdSe_cadmoselite.cif
similarity index 100%
rename from src/diffpy/srreal/tests/testdata/CdSe_cadmoselite.cif
rename to tests/testdata/CdSe_cadmoselite.cif
diff --git a/src/diffpy/srreal/tests/testdata/CdSe_cadmoselite_N.fgr b/tests/testdata/CdSe_cadmoselite_N.fgr
similarity index 100%
rename from src/diffpy/srreal/tests/testdata/CdSe_cadmoselite_N.fgr
rename to tests/testdata/CdSe_cadmoselite_N.fgr
diff --git a/src/diffpy/srreal/tests/testdata/CdSe_cadmoselite_X.fgr b/tests/testdata/CdSe_cadmoselite_X.fgr
similarity index 100%
rename from src/diffpy/srreal/tests/testdata/CdSe_cadmoselite_X.fgr
rename to tests/testdata/CdSe_cadmoselite_X.fgr
diff --git a/src/diffpy/srreal/tests/testdata/Ni-fit.fgr b/tests/testdata/Ni-fit.fgr
similarity index 100%
rename from src/diffpy/srreal/tests/testdata/Ni-fit.fgr
rename to tests/testdata/Ni-fit.fgr
diff --git a/src/diffpy/srreal/tests/testdata/Ni.cif b/tests/testdata/Ni.cif
similarity index 100%
rename from src/diffpy/srreal/tests/testdata/Ni.cif
rename to tests/testdata/Ni.cif
diff --git a/src/diffpy/srreal/tests/testdata/Ni.stru b/tests/testdata/Ni.stru
similarity index 100%
rename from src/diffpy/srreal/tests/testdata/Ni.stru
rename to tests/testdata/Ni.stru
diff --git a/src/diffpy/srreal/tests/testdata/Ni_primitive.stru b/tests/testdata/Ni_primitive.stru
similarity index 100%
rename from src/diffpy/srreal/tests/testdata/Ni_primitive.stru
rename to tests/testdata/Ni_primitive.stru
diff --git a/src/diffpy/srreal/tests/testdata/TiO2_rutile-fit.cif b/tests/testdata/TiO2_rutile-fit.cif
similarity index 100%
rename from src/diffpy/srreal/tests/testdata/TiO2_rutile-fit.cif
rename to tests/testdata/TiO2_rutile-fit.cif
diff --git a/src/diffpy/srreal/tests/testdata/TiO2_rutile-fit.fgr b/tests/testdata/TiO2_rutile-fit.fgr
similarity index 100%
rename from src/diffpy/srreal/tests/testdata/TiO2_rutile-fit.fgr
rename to tests/testdata/TiO2_rutile-fit.fgr
diff --git a/src/diffpy/srreal/tests/testdata/TiO2_rutile-fit.stru b/tests/testdata/TiO2_rutile-fit.stru
similarity index 100%
rename from src/diffpy/srreal/tests/testdata/TiO2_rutile-fit.stru
rename to tests/testdata/TiO2_rutile-fit.stru
diff --git a/src/diffpy/srreal/tests/testdata/rutile.cif b/tests/testdata/rutile.cif
similarity index 100%
rename from src/diffpy/srreal/tests/testdata/rutile.cif
rename to tests/testdata/rutile.cif
diff --git a/src/diffpy/srreal/tests/testdata/silicon.cif b/tests/testdata/silicon.cif
similarity index 100%
rename from src/diffpy/srreal/tests/testdata/silicon.cif
rename to tests/testdata/silicon.cif
diff --git a/src/diffpy/srreal/tests/testdata/sphalerite.cif b/tests/testdata/sphalerite.cif
similarity index 100%
rename from src/diffpy/srreal/tests/testdata/sphalerite.cif
rename to tests/testdata/sphalerite.cif
diff --git a/src/diffpy/srreal/tests/testutils.py b/tests/testutils.py
similarity index 68%
rename from src/diffpy/srreal/tests/testutils.py
rename to tests/testutils.py
index 8cbb3ec..5f594af 100644
--- a/src/diffpy/srreal/tests/testutils.py
+++ b/tests/testutils.py
@@ -8,67 +8,23 @@
 
 import numpy
 
+import diffpy.structure as mod_structure
 from diffpy.srreal.structureadapter import (
     AtomicStructureAdapter,
     CrystalStructureAdapter,
     PeriodicStructureAdapter,
     StructureAdapter,
 )
-from diffpy.srreal.structureconverters import convertObjCrystCrystal
-from diffpy.srreal.tests import logger
-
-# Deprecated in 1.3 - import of old camel-case diffpy.Structure names.
-# TODO drop this in version 1.4.
-
-try:
-    import diffpy.structure as mod_structure
-    from diffpy.structure.parsers import getParser
-except ImportError as e:
-    try:
-        import diffpy.Structure as mod_structure
-        from diffpy.Structure.Parsers import getParser
-    except ImportError:
-        raise e
-    del e
-
-# Resolve availability of optional packages.
-
-# pyobjcryst
-
-_msg_nopyobjcryst = "No module named 'pyobjcryst'"
-try:
-    import pyobjcryst.crystal
-
-    convertObjCrystCrystal(pyobjcryst.crystal.Crystal())
-    has_pyobjcryst = True
-except ImportError:
-    has_pyobjcryst = False
-    logger.warning("Cannot import pyobjcryst, pyobjcryst tests skipped.")
-except TypeError:
-    has_pyobjcryst = False
-    logger.warning("Compiled without ObjCryst, pyobjcryst tests skipped.")
-
-# periodictable
-
-_msg_noperiodictable = "No module named 'periodictable'"
-try:
-    import periodictable
-
-    has_periodictable = True
-    # silence the pyflakes syntax checker
-    del periodictable
-except ImportError:
-    has_periodictable = False
-    logger.warning("Cannot import periodictable, periodictable tests skipped.")
+from diffpy.structure.parsers import getParser
 
 # helper functions
 
 
 def datafile(filename):
-    from pkg_resources import resource_filename
+    from pathlib import Path
 
-    rv = resource_filename(__name__, "testdata/" + filename)
-    return rv
+    rv = Path(__file__).parent / "testdata" / filename
+    return str(rv)
 
 
 def loadObjCrystCrystal(filename):
@@ -108,6 +64,15 @@ def pickle_with_attr(obj, **attr):
     return rv
 
 
+def _maxNormDiff(yobs, ycalc):
+    """Returned maximum difference normalized by RMS of the yobs."""
+    yobsa = numpy.array(yobs)
+    obsmax = numpy.max(numpy.fabs(yobsa)) or 1
+    ynmdiff = (yobsa - ycalc) / obsmax
+    rv = max(numpy.fabs(ynmdiff))
+    return rv
+
+
 # helper class for testing overloading of StructureAdapter