add interface tests and fix behaviour

Author: DracoLi

x/blockdb/database.go

@@ -303,7 +303,7 @@ func (s *Database) Close() error {
 	defer s.closeMu.Unlock()
 
 	if s.closed {
-		return nil
+		return database.ErrClosed
 	}
 	s.closed = true
 
@@ -524,6 +524,10 @@ func (s *Database) Get(height BlockHeight) (BlockData, error) {
 		return nil, fmt.Errorf("checksum mismatch: calculated %d, stored %d", calculatedChecksum, bh.Checksum)
 	}
 
+	if len(decompressed) == 0 {
+		return nil, nil
+	}
+
 	return decompressed, nil
 }
 

x/blockdb/database_test.go

@@ -18,10 +18,25 @@ import (
 	"github.com/stretchr/testify/require"
 
 	"github.com/ava-labs/avalanchego/cache/lru"
+	"github.com/ava-labs/avalanchego/database"
+	"github.com/ava-labs/avalanchego/database/heightindexdb/dbtest"
 	"github.com/ava-labs/avalanchego/utils/compression"
 	"github.com/ava-labs/avalanchego/utils/logging"
 )
 
+func TestInterface(t *testing.T) {
+	for name, test := range dbtest.Tests {
+		t.Run(name, func(t *testing.T) {
+			test(t, func() database.HeightIndex {
+				tempDir := t.TempDir()
+				db, err := New(DefaultConfig().WithDir(tempDir), logging.NoLog{})
+				require.NoError(t, err)
+				return db
+			})
+		})
+	}
+}
+
 func TestNew_Params(t *testing.T) {
 	tempDir := t.TempDir()
 	tests := []struct {