refactor test_connect for new test suite

Provides mixins for TestCosmology to test the descriptors

Signed-off-by: Nathaniel Starkman (@nstarman) <nstarkman@protonmail.com>

astropy/cosmology/core.py

@@ -264,7 +264,7 @@ def __new__(cls, *args, **kwargs):
 
         return self
 
-    def __init__(self, *args, name=None, meta=None, **kwargs):
+    def __init__(self, name=None, meta=None):
         self._name = name
         self.meta.update(meta or {})
 

astropy/cosmology/io/tests/test_mapping.py

@@ -12,7 +12,7 @@
 
 class CosmologyWithKwargs(Cosmology):
     def __init__(self, name="cosmology with kwargs", meta=None, **kwargs):
-        super().__init__(name=name, meta=meta, **kwargs)
+        super().__init__(name=name, meta=meta)
 
 
 cosmo_instances = [

astropy/cosmology/tests/conftest.py

@@ -5,13 +5,89 @@
 ##############################################################################
 # IMPORTS
 
+# STDLIB
+import json
+import os
+
 import pytest
 
+import astropy.units as u
 from astropy.cosmology import core
+from astropy.cosmology.core import Cosmology
+from astropy.utils.misc import isiterable
 
 ###############################################################################
+# FUNCTIONS
+
+
+def read_json(filename, **kwargs):
+    """Read JSON.
+
+    Parameters
+    ----------
+    filename : str
+    **kwargs
+        Keyword arguments into :meth:`~astropy.cosmology.Cosmology.from_format`
+
+    Returns
+    -------
+    `~astropy.cosmology.Cosmology` instance
+
+    """
+    # read
+    if isinstance(filename, (str, bytes, os.PathLike)):
+        with open(filename, "r") as file:
+            data = file.read()
+    else:  # file-like : this also handles errors in dumping
+        data = filename.read()
+
+    mapping = json.loads(data)  # parse json mappable to dict
+
+    # deserialize Quantity
+    for k, v in mapping.items():
+        if isinstance(v, dict) and "value" in v and "unit" in v:
+            mapping[k] = u.Quantity(v["value"], v["unit"])
+    for k, v in mapping.get("meta", {}).items():  # also the metadata
+        if isinstance(v, dict) and "value" in v and "unit" in v:
+            mapping["meta"][k] = u.Quantity(v["value"], v["unit"])
+
+    return Cosmology.from_format(mapping, **kwargs)
 
 
+def write_json(cosmology, file, *, overwrite=False):
+    """Write Cosmology to JSON.
+
+    Parameters
+    ----------
+    cosmology : `astropy.cosmology.Cosmology` subclass instance
+    file : path-like or file-like
+    overwrite : bool (optional, keyword-only)
+    """
+    data = cosmology.to_format("mapping")  # start by turning into dict
+    data["cosmology"] = data["cosmology"].__qualname__
+
+    # serialize Quantity
+    for k, v in data.items():
+        if isinstance(v, u.Quantity):
+            data[k] = {"value": v.value.tolist(), "unit": str(v.unit)}
+    for k, v in data.get("meta", {}).items():  # also serialize the metadata
+        if isinstance(v, u.Quantity):
+            data["meta"][k] = {"value": v.value.tolist(), "unit": str(v.unit)}
+
+    # check that file exists and whether to overwrite.
+    if os.path.exists(file) and not overwrite:
+        raise IOError(f"{file} exists. Set 'overwrite' to write over.")
+    with open(file, "w") as write_file:
+        json.dump(data, write_file)
+
+
+def json_identify(origin, filepath, fileobj, *args, **kwargs):
+    return filepath is not None and filepath.endswith(".json")
+
+
+###############################################################################
+# FIXTURES
+
 @pytest.fixture
 def clean_registry():
     # TODO! with monkeypatch instead for thread safety.