test: add mysql connector tests

In order to increase the coverage of the patch, I added the following
tests:

- connection metrics can't be registered
- duplicate db names are used to create the datastore

Signed-off-by: leonnicolas <[email protected]>

Author: leonnicolas

internal/datastore/mysql/datastore_test.go

@@ -6,6 +6,7 @@ package mysql
 import (
 	"context"
 	"database/sql"
+	"errors"
 	"fmt"
 	"testing"
 	"time"
@@ -132,6 +133,24 @@ func TestMySQLRevisionTimestamps(t *testing.T) {
 	t.Run("TransactionTimestamps", createDatastoreTest(b, TransactionTimestampsTest, defaultOptions...))
 }
 
+func multiDataStoreWithDuplicateDBNames(t *testing.T, b testdatastore.RunningEngineForTest, errMsg string) func(*testing.T) {
+	return func(t *testing.T) {
+		ctx := t.Context()
+
+		ds := b.NewDatastore(t, func(engine, uri string) datastore.Datastore {
+			ds, err := newMySQLDatastore(ctx, uri, primaryInstanceID, WithEnablePrometheusStats(true))
+			require.NoError(t, err)
+
+			_, err = newMySQLDatastore(ctx, uri, primaryInstanceID, WithEnablePrometheusStats(true))
+			require.Error(t, err)
+			require.ErrorContains(t, err, errMsg)
+
+			return ds
+		})
+		defer failOnError(t, ds.Close)
+	}
+}
+
 func additionalMySQLTests(t *testing.T, b testdatastore.RunningEngineForTest) {
 	{
 		reg := prometheus.NewRegistry()
@@ -152,13 +171,41 @@ func additionalMySQLTests(t *testing.T, b testdatastore.RunningEngineForTest) {
 	t.Run("QuantizedRevisions", func(t *testing.T) {
 		QuantizedRevisionTest(t, b)
 	})
+	{
+		reg := &unregisterable{*prometheus.NewRegistry()}
+		prometheus.DefaultGatherer = reg
+		prometheus.DefaultRegisterer = reg
+	}
+	t.Run("DatastoreWithUnregisterableRegistry", func(t *testing.T) {
+		_ = b.NewDatastore(t, func(engine, uri string) datastore.Datastore {
+			ds, err := newMySQLDatastore(t.Context(), uri, primaryInstanceID, WithEnablePrometheusStats(true))
+			require.Error(t, err)
+			require.ErrorContains(t, err, "NewMySQLDatastore: unable to instrument connector.")
+			require.Nil(t, ds)
+			return ds
+		})
+	})
 	t.Run("Locking", createMultiDatastoreTest(b, LockingTest, defaultOptions...))
 	{
 		reg := prometheus.NewRegistry()
 		prometheus.DefaultGatherer = reg
 		prometheus.DefaultRegisterer = reg
 	}
-	t.Run("InstrumentedLocking", createMultiDatastoreTest(b, LockingTest, append(defaultOptions, WithEnablePrometheusStats(true))...))
+	t.Run("MultiDatastoreWithPrometheus", createMultiDatastoreTest(b, func(t *testing.T, ds1 datastore.Datastore, ds2 datastore.Datastore) {}, append(defaultOptions, WithEnablePrometheusStats(true))...))
+	{
+		reg := prometheus.NewRegistry()
+		prometheus.DefaultGatherer = reg
+		prometheus.DefaultRegisterer = reg
+	}
+	t.Run("MultiDatastoreWithPrometheusWithDuplicateDBNames", multiDataStoreWithDuplicateDBNames(t, b, "duplicate metrics collector registration attempted"))
+}
+
+type unregisterable struct {
+	prometheus.Registry
+}
+
+func (*unregisterable) Register(prometheus.Collector) error {
+	return errors.New("unregisterable")
 }
 
 func LockingTest(t *testing.T, ds datastore.Datastore, ds2 datastore.Datastore) {