Implement basic automated tests targeting the validate_json function

tests/test_util/README.md

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+This directory contains file related to testing code written in the `nmdc_runtime/util.py` file.
+
+I named the directory "`test_util`" in an attempt to follow the naming convention of the other test directories.
+In its name, "`test`" is a verb and "`util`" is a noun (i.e. "to test the utility"). This is in contrast to the file 
+`../test_util.py`, in whose name "`test`" is an adjective and "`util`" is a noun (i.e. "a test-related utility").

tests/test_util/test_util.py

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+from nmdc_runtime.api.db.mongo import get_mongo_db
+from nmdc_runtime.util import validate_json
+
+# Tip: At the time of this writing, you can run the tests in this file without running other tests in this repo,
+#      by issuing the following command from the root directory of the repository:
+#      ```
+#      $ pytest tests/test_util/test_util.py
+#      ```
+
+
+def test_validate_json():
+    # Get a reference to the MongoDB database, since the `validate_json` function requires
+    # it to be passed in as a parameter.
+    mdb = get_mongo_db()
+
+    # Define a reusable dictionary that matches the value the `validate_json` function
+    # returns when it considers the input to be valid.
+    ok_result = {"result": "All Okay!"}
+
+    # Test: An empty outer dictionary is valid.
+    database_dict = {}
+    result = validate_json(in_docs=database_dict, mdb=mdb)
+    assert result == ok_result
+
+    # Test: An empty collection is valid.
+    database_dict = {"study_set": []}
+    result = validate_json(in_docs=database_dict, mdb=mdb)
+    assert result == ok_result
+
+    # Test: Two empty collections is valid.
+    database_dict = {"biosample_set": [], "study_set": []}
+    result = validate_json(in_docs=database_dict, mdb=mdb)
+    assert result == ok_result
+
+    # Test: A schema-compliant document is valid.
+    database_dict = {
+        "study_set": [
+            {
+                "id": "nmdc:sty-00-000001",
+                "type": "nmdc:Study",
+                "study_category": "research_study",
+            }
+        ]
+    }
+    result = validate_json(in_docs=database_dict, mdb=mdb)
+    assert result == ok_result
+
+    # Test: Multiple schema-compliant documents are valid.
+    database_dict = {
+        "study_set": [
+            {
+                "id": "nmdc:sty-00-000001",
+                "type": "nmdc:Study",
+                "study_category": "research_study",
+            },
+            {
+                "id": "nmdc:sty-00-000002",
+                "type": "nmdc:Study",
+                "study_category": "research_study",
+            },
+        ]
+    }
+    result = validate_json(in_docs=database_dict, mdb=mdb)
+    assert result == ok_result
+
+    # Test: The function reports an error for the schema-defiant document.
+    database_dict = {
+        "study_set": [
+            {
+                "id": "nmdc:OTHER-00-000001",
+                "type": "nmdc:Study",
+                "study_category": "research_study",
+            },
+        ]
+    }
+    result = validate_json(in_docs=database_dict, mdb=mdb)
+    assert result["result"] == "errors"
+    assert "study_set" in result["detail"]
+    assert len(result["detail"]["study_set"]) == 1
+
+    # Test: The function reports an error for each schema-defiant document.
+    database_dict = {
+        "study_set": [
+            {
+                "id": "nmdc:OTHER-00-000001",
+                "type": "nmdc:Study",
+                "study_category": "research_study",
+            },
+            {
+                "id": "nmdc:OTHER-00-000002",
+                "type": "nmdc:Study",
+                "study_category": "research_study",
+            },
+        ]
+    }
+    result = validate_json(in_docs=database_dict, mdb=mdb)
+    assert result["result"] == "errors"
+    assert "study_set" in result["detail"]
+    assert len(result["detail"]["study_set"]) == 2