diff --git a/django_spanner/base.py b/django_spanner/base.py
index 70f5b1ba39..f5d2c835d5 100644
--- a/django_spanner/base.py
+++ b/django_spanner/base.py
@@ -18,62 +18,62 @@ from .validation import DatabaseValidation
 
 
 class DatabaseWrapper(BaseDatabaseWrapper):
-    vendor = 'spanner'
-    display_name = 'Cloud Spanner'
+    vendor = "spanner"
+    display_name = "Cloud Spanner"
 
     # Mapping of Field objects to their column types.
     # https://cloud.google.com/spanner/docs/data-types#date-type
     data_types = {
-        'AutoField': 'INT64',
-        'BigAutoField': 'INT64',
-        'BinaryField': 'BYTES(MAX)',
-        'BooleanField': 'BOOL',
-        'CharField': 'STRING(%(max_length)s)',
-        'DateField': 'DATE',
-        'DateTimeField': 'TIMESTAMP',
-        'DecimalField': 'FLOAT64',
-        'DurationField': 'INT64',
-        'EmailField': 'STRING(%(max_length)s)',
-        'FileField': 'STRING(%(max_length)s)',
-        'FilePathField': 'STRING(%(max_length)s)',
-        'FloatField': 'FLOAT64',
-        'IntegerField': 'INT64',
-        'BigIntegerField': 'INT64',
-        'IPAddressField': 'STRING(15)',
-        'GenericIPAddressField': 'STRING(39)',
-        'NullBooleanField': 'BOOL',
-        'OneToOneField': 'INT64',
-        'PositiveIntegerField': 'INT64',
-        'PositiveSmallIntegerField': 'INT64',
-        'SlugField': 'STRING(%(max_length)s)',
-        'SmallAutoField': 'INT64',
-        'SmallIntegerField': 'INT64',
-        'TextField': 'STRING(MAX)',
-        'TimeField': 'TIMESTAMP',
-        'UUIDField': 'STRING(32)',
+        "AutoField": "INT64",
+        "BigAutoField": "INT64",
+        "BinaryField": "BYTES(MAX)",
+        "BooleanField": "BOOL",
+        "CharField": "STRING(%(max_length)s)",
+        "DateField": "DATE",
+        "DateTimeField": "TIMESTAMP",
+        "DecimalField": "FLOAT64",
+        "DurationField": "INT64",
+        "EmailField": "STRING(%(max_length)s)",
+        "FileField": "STRING(%(max_length)s)",
+        "FilePathField": "STRING(%(max_length)s)",
+        "FloatField": "FLOAT64",
+        "IntegerField": "INT64",
+        "BigIntegerField": "INT64",
+        "IPAddressField": "STRING(15)",
+        "GenericIPAddressField": "STRING(39)",
+        "NullBooleanField": "BOOL",
+        "OneToOneField": "INT64",
+        "PositiveIntegerField": "INT64",
+        "PositiveSmallIntegerField": "INT64",
+        "SlugField": "STRING(%(max_length)s)",
+        "SmallAutoField": "INT64",
+        "SmallIntegerField": "INT64",
+        "TextField": "STRING(MAX)",
+        "TimeField": "TIMESTAMP",
+        "UUIDField": "STRING(32)",
     }
     operators = {
-        'exact': '= %s',
-        'iexact': 'REGEXP_CONTAINS(%s, %%%%s)',
+        "exact": "= %s",
+        "iexact": "REGEXP_CONTAINS(%s, %%%%s)",
         # contains uses REGEXP_CONTAINS instead of LIKE to allow
         # DatabaseOperations.prep_for_like_query() to do regular expression
         # escaping. prep_for_like_query() is called for all the lookups that
         # use REGEXP_CONTAINS except regex/iregex (see
         # django.db.models.lookups.PatternLookup).
-        'contains':  'REGEXP_CONTAINS(%s, %%%%s)',
-        'icontains': 'REGEXP_CONTAINS(%s, %%%%s)',
-        'gt': '> %s',
-        'gte': '>= %s',
-        'lt': '< %s',
-        'lte': '<= %s',
+        "contains": "REGEXP_CONTAINS(%s, %%%%s)",
+        "icontains": "REGEXP_CONTAINS(%s, %%%%s)",
+        "gt": "> %s",
+        "gte": ">= %s",
+        "lt": "< %s",
+        "lte": "<= %s",
         # Using REGEXP_CONTAINS instead of STARTS_WITH and ENDS_WITH for the
         # same reasoning as described above for 'contains'.
-        'startswith': 'REGEXP_CONTAINS(%s, %%%%s)',
-        'endswith': 'REGEXP_CONTAINS(%s, %%%%s)',
-        'istartswith': 'REGEXP_CONTAINS(%s, %%%%s)',
-        'iendswith': 'REGEXP_CONTAINS(%s, %%%%s)',
-        'regex': 'REGEXP_CONTAINS(%s, %%%%s)',
-        'iregex': 'REGEXP_CONTAINS(%s, %%%%s)',
+        "startswith": "REGEXP_CONTAINS(%s, %%%%s)",
+        "endswith": "REGEXP_CONTAINS(%s, %%%%s)",
+        "istartswith": "REGEXP_CONTAINS(%s, %%%%s)",
+        "iendswith": "REGEXP_CONTAINS(%s, %%%%s)",
+        "regex": "REGEXP_CONTAINS(%s, %%%%s)",
+        "iregex": "REGEXP_CONTAINS(%s, %%%%s)",
     }
 
     # pattern_esc is used to generate SQL pattern lookup clauses when the
@@ -81,16 +81,18 @@ class DatabaseWrapper(BaseDatabaseWrapper):
     # expression or the result of a bilateral transformation). In those cases,
     # special characters for REGEXP_CONTAINS operators (e.g. \, *, _) must be
     # escaped on database side.
-    pattern_esc = r'REPLACE(REPLACE(REPLACE({}, "\\", "\\\\"), "%%", r"\%%"), "_", r"\_")'
+    pattern_esc = (
+        r'REPLACE(REPLACE(REPLACE({}, "\\", "\\\\"), "%%", r"\%%"), "_", r"\_")'
+    )
     # These are all no-ops in favor of using REGEXP_CONTAINS in the customized
     # lookups.
     pattern_ops = {
-        'contains': '',
-        'icontains': '',
-        'startswith': '',
-        'istartswith': '',
-        'endswith': '',
-        'iendswith': '',
+        "contains": "",
+        "icontains": "",
+        "startswith": "",
+        "istartswith": "",
+        "endswith": "",
+        "iendswith": "",
     }
 
     Database = Database
@@ -104,7 +106,7 @@ class DatabaseWrapper(BaseDatabaseWrapper):
 
     @property
     def instance(self):
-        return spanner.Client().instance(self.settings_dict['INSTANCE'])
+        return spanner.Client().instance(self.settings_dict["INSTANCE"])
 
     @property
     def _nodb_connection(self):
@@ -112,11 +114,11 @@ class DatabaseWrapper(BaseDatabaseWrapper):
 
     def get_connection_params(self):
         return {
-            'project': self.settings_dict['PROJECT'],
-            'instance': self.settings_dict['INSTANCE'],
-            'database': self.settings_dict['NAME'],
-            'user_agent': 'django_spanner/0.0.1',
-            **self.settings_dict['OPTIONS'],
+            "project": self.settings_dict["PROJECT"],
+            "instance_id": self.settings_dict["INSTANCE"],
+            "database_id": self.settings_dict["NAME"],
+            "user_agent": "django_spanner/0.0.1",
+            **self.settings_dict["OPTIONS"],
         }
 
     def get_new_connection(self, conn_params):
@@ -137,7 +139,7 @@ class DatabaseWrapper(BaseDatabaseWrapper):
             return False
         try:
             # Use a cursor directly, bypassing Django's utilities.
-            self.connection.cursor().execute('SELECT 1')
+            self.connection.cursor().execute("SELECT 1")
         except Database.Error:
             return False
         else:
diff --git a/setup.cfg b/setup.cfg
index f9e8dff043..43c26175ef 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -2,8 +2,10 @@
 max-line-length = 119
 
 [isort]
+use_parentheses=True
 combine_as_imports = true
 default_section = THIRDPARTY
 include_trailing_comma = true
+force_grid_wrap=0
 line_length = 79
-multi_line_output = 5
+multi_line_output = 3
\ No newline at end of file
diff --git a/spanner_dbapi/__init__.py b/spanner_dbapi/__init__.py
index f5d349a655..58037106ca 100644
--- a/spanner_dbapi/__init__.py
+++ b/spanner_dbapi/__init__.py
@@ -4,83 +4,122 @@
 # license that can be found in the LICENSE file or at
 # https://developers.google.com/open-source/licenses/bsd
 
-from google.cloud import spanner_v1 as spanner
+"""Connection-based DB API for Cloud Spanner."""
+
+from google.cloud import spanner_v1
 
 from .connection import Connection
-# These need to be included in the top-level package for PEP-0249 DB API v2.
 from .exceptions import (
-    DatabaseError, DataError, Error, IntegrityError, InterfaceError,
-    InternalError, NotSupportedError, OperationalError, ProgrammingError,
+    DatabaseError,
+    DataError,
+    Error,
+    IntegrityError,
+    InterfaceError,
+    InternalError,
+    NotSupportedError,
+    OperationalError,
+    ProgrammingError,
     Warning,
 )
 from .parse_utils import get_param_types
 from .types import (
-    BINARY, DATETIME, NUMBER, ROWID, STRING, Binary, Date, DateFromTicks, Time,
-    TimeFromTicks, Timestamp, TimestampFromTicks,
+    BINARY,
+    DATETIME,
+    NUMBER,
+    ROWID,
+    STRING,
+    Binary,
+    Date,
+    DateFromTicks,
+    Time,
+    TimeFromTicks,
+    Timestamp,
+    TimestampFromTicks,
 )
 from .version import google_client_info
 
-# Globals that MUST be defined ###
-apilevel = "2.0"  # Implements the Python Database API specification 2.0 version.
-# We accept arguments in the format '%s' aka ANSI C print codes.
-# as per https://www.python.org/dev/peps/pep-0249/#paramstyle
-paramstyle = 'format'
-# Threads may share the module but not connections. This is a paranoid threadsafety level,
-# but it is necessary for starters to use when debugging failures. Eventually once transactions
-# are working properly, we'll update the threadsafety level.
+apilevel = "2.0"  # supports DP-API 2.0 level.
+paramstyle = "format"  # ANSI C printf format codes, e.g. ...WHERE name=%s.
+
+# Threads may share the module, but not connections. This is a paranoid threadsafety
+# level, but it is necessary for starters to use when debugging failures.
+# Eventually once transactions are working properly, we'll update the
+# threadsafety level.
 threadsafety = 1
 
 
-def connect(project=None, instance=None, database=None, credentials_uri=None, user_agent=None):
+def connect(instance_id, database_id, project=None, credentials=None, user_agent=None):
     """
-    Connect to Cloud Spanner.
+    Create a connection to Cloud Spanner database.
 
-    Args:
-        project: The id of a project that already exists.
-        instance: The id of an instance that already exists.
-        database: The name of a database that already exists.
-        credentials_uri: An optional string specifying where to retrieve the service
-                         account JSON for the credentials to connect to Cloud Spanner.
+    :type instance_id: :class:`str`
+    :param instance_id: ID of the instance to connect to.
 
-    Returns:
-        The Connection object associated to the Cloud Spanner instance.
+    :type database_id: :class:`str`
+    :param database_id: The name of the database to connect to.
 
-    Raises:
-        Error if it encounters any unexpected inputs.
-    """
-    if not project:
-        raise Error("'project' is required.")
-    if not instance:
-        raise Error("'instance' is required.")
-    if not database:
-        raise Error("'database' is required.")
+    :type project: :class:`str`
+    :param project: (Optional) The ID of the project which owns the
+                    instances, tables and data. If not provided, will
+                    attempt to determine from the environment.
 
-    client_kwargs = {
-        'project': project,
-        'client_info': google_client_info(user_agent),
-    }
-    if credentials_uri:
-        client = spanner.Client.from_service_account_json(credentials_uri, **client_kwargs)
-    else:
-        client = spanner.Client(**client_kwargs)
+    :type credentials: :class:`google.auth.credentials.Credentials`
+    :param credentials: (Optional) The authorization credentials to attach to requests.
+                        These credentials identify this application to the service.
+                        If none are specified, the client will attempt to ascertain
+                        the credentials from the environment.
+
+    :rtype: :class:`google.cloud.spanner_dbapi.connection.Connection`
+    :returns: Connection object associated with the given Cloud Spanner resource.
+
+    :raises: :class:`ValueError` in case of given instance/database
+             doesn't exist.
+    """
+    client = spanner_v1.Client(
+        project=project,
+        credentials=credentials,
+        client_info=google_client_info(user_agent),
+    )
 
-    client_instance = client.instance(instance)
-    if not client_instance.exists():
-        raise ProgrammingError("instance '%s' does not exist." % instance)
+    instance = client.instance(instance_id)
+    if not instance.exists():
+        raise ValueError("instance '%s' does not exist." % instance_id)
 
-    db = client_instance.database(database, pool=spanner.pool.BurstyPool())
-    if not db.exists():
-        raise ProgrammingError("database '%s' does not exist." % database)
+    database = instance.database(database_id, pool=spanner_v1.pool.BurstyPool())
+    if not database.exists():
+        raise ValueError("database '%s' does not exist." % database_id)
 
-    return Connection(db)
+    return Connection(database)
 
 
 __all__ = [
-    'DatabaseError', 'DataError', 'Error', 'IntegrityError', 'InterfaceError',
-    'InternalError', 'NotSupportedError', 'OperationalError', 'ProgrammingError',
-    'Warning', 'DEFAULT_USER_AGENT', 'apilevel', 'connect', 'paramstyle', 'threadsafety',
-    'get_param_types',
-    'Binary', 'Date', 'DateFromTicks', 'Time', 'TimeFromTicks', 'Timestamp',
-    'TimestampFromTicks',
-    'BINARY', 'STRING', 'NUMBER', 'DATETIME', 'ROWID', 'TimestampStr',
+    "DatabaseError",
+    "DataError",
+    "Error",
+    "IntegrityError",
+    "InterfaceError",
+    "InternalError",
+    "NotSupportedError",
+    "OperationalError",
+    "ProgrammingError",
+    "Warning",
+    "DEFAULT_USER_AGENT",
+    "apilevel",
+    "connect",
+    "paramstyle",
+    "threadsafety",
+    "get_param_types",
+    "Binary",
+    "Date",
+    "DateFromTicks",
+    "Time",
+    "TimeFromTicks",
+    "Timestamp",
+    "TimestampFromTicks",
+    "BINARY",
+    "STRING",
+    "NUMBER",
+    "DATETIME",
+    "ROWID",
+    "TimestampStr",
 ]

diff --git a/tests/spanner_dbapi/test_connect.py b/tests/spanner_dbapi/test_connect.py
new file mode 100644
index 0000000000..64eaf8cd7d
--- /dev/null
+++ b/tests/spanner_dbapi/test_connect.py
@@ -0,0 +1,97 @@
+# Copyright 2020 Google LLC
+#
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file or at
+# https://developers.google.com/open-source/licenses/bsd
+
+"""connect() module function unit tests."""
+
+import unittest
+from unittest import mock
+
+import google.auth.credentials
+from google.api_core.gapic_v1.client_info import ClientInfo
+from spanner_dbapi import connect, Connection
+
+
+def _make_credentials():
+    class _CredentialsWithScopes(
+        google.auth.credentials.Credentials, google.auth.credentials.Scoped
+    ):
+        pass
+
+    return mock.Mock(spec=_CredentialsWithScopes)
+
+
+class Test_connect(unittest.TestCase):
+    def test_connect(self):
+        PROJECT = "test-project"
+        USER_AGENT = "user-agent"
+        CREDENTIALS = _make_credentials()
+        CLIENT_INFO = ClientInfo(user_agent=USER_AGENT)
+
+        with mock.patch("spanner_dbapi.spanner_v1.Client") as client_mock:
+            with mock.patch(
+                "spanner_dbapi.google_client_info", return_value=CLIENT_INFO
+            ) as client_info_mock:
+
+                connection = connect(
+                    "test-instance", "test-database", PROJECT, CREDENTIALS, USER_AGENT
+                )
+
+                self.assertIsInstance(connection, Connection)
+                client_info_mock.assert_called_once_with(USER_AGENT)
+
+            client_mock.assert_called_once_with(
+                project=PROJECT, credentials=CREDENTIALS, client_info=CLIENT_INFO
+            )
+
+    def test_instance_not_found(self):
+        with mock.patch(
+            "google.cloud.spanner_v1.instance.Instance.exists", return_value=False
+        ) as exists_mock:
+
+            with self.assertRaises(ValueError):
+                connect("test-instance", "test-database")
+
+            exists_mock.assert_called_once_with()
+
+    def test_database_not_found(self):
+        with mock.patch(
+            "google.cloud.spanner_v1.instance.Instance.exists", return_value=True
+        ):
+            with mock.patch(
+                "google.cloud.spanner_v1.database.Database.exists", return_value=False
+            ) as exists_mock:
+
+                with self.assertRaises(ValueError):
+                    connect("test-instance", "test-database")
+
+                exists_mock.assert_called_once_with()
+
+    def test_connect_instance_id(self):
+        INSTANCE = "test-instance"
+
+        with mock.patch(
+            "google.cloud.spanner_v1.client.Client.instance"
+        ) as instance_mock:
+            connection = connect(INSTANCE, "test-database")
+
+            instance_mock.assert_called_once_with(INSTANCE)
+
+        self.assertIsInstance(connection, Connection)
+
+    def test_connect_database_id(self):
+        DATABASE = "test-database"
+
+        with mock.patch(
+            "google.cloud.spanner_v1.instance.Instance.database"
+        ) as database_mock:
+            with mock.patch(
+                "google.cloud.spanner_v1.instance.Instance.exists", return_value=True
+            ):
+                connection = connect("test-instance", DATABASE)
+
+                database_mock.assert_called_once_with(DATABASE, pool=mock.ANY)
+
+        self.assertIsInstance(connection, Connection)

connect() surface issues
Looking at `connect()` function, there are several things which are raising questions.

**project arg:**
 `project` is set as an optional arg: https://github.com/googleapis/python-spanner-django/blob/11222db2f82fd50ca87010321ded0b39021eb884/spanner_dbapi/__init__.py#L34 But few lines lower it is checked for existence (thus, it's required, not optional): https://github.com/googleapis/python-spanner-django/blob/11222db2f82fd50ca87010321ded0b39021eb884/spanner_dbapi/__init__.py#L51-L52 It seems to be pointless, as this arg is only passed to Spanner client, and the original Spanner client can handle an omitted project: it'll use `google.auth.default()` function to designate the project id from the environment. With this, I'd propose to drop this check and use `project` arg in the way of the original Spanner client.

**instance and database args:**
They are optional by definition, but in fact both are required. Probably, they should become required in definition (the function signature will be `connect(instance, database, project=None, credentials_uri=None, user_agent=None):`), so these checks could be dropped:
https://github.com/googleapis/python-spanner-django/blob/11222db2f82fd50ca87010321ded0b39021eb884/spanner_dbapi/__init__.py#L53-L56

**credentials_uri arg:**
This arg looks divergent from how the original Spanner client is dealing with credentials:
https://github.com/googleapis/python-spanner/blob/b6b0348f5870f55c88b3cae44e229325fd755b26/google/cloud/spanner_v1/client.py#L123-L129

I'd propose to change this arg to use `google.auth.credentials.Credentials` class as it's done in the original Spanner client.
tests/spanner_dbapi/test_connect.py::Test_connect::test_connect