Add negative tests for FetchBlockShaByHeight.

This commit adds tests to ensure FetchBlockShaByHeight returns expected
errors when invalid heights are specified.

interface_test.go

@@ -5,11 +5,35 @@
 package btcdb_test
 
 import (
+	"github.com/conformal/btcdb"
 	"github.com/davecgh/go-spew/spew"
 	"reflect"
 	"testing"
 )
 
+// testFetchBlockShaByHeightErrors ensures FetchBlockShaByHeight handles invalid
+// heights correctly.
+func testFetchBlockShaByHeightErrors(t *testing.T, dbType string, db btcdb.Db, numBlocks int64) bool {
+	tests := []int64{-1, numBlocks, numBlocks + 1}
+	for i, wantHeight := range tests {
+		hashFromDb, err := db.FetchBlockShaByHeight(wantHeight)
+		if err == nil {
+			t.Errorf("FetchBlockShaByHeight #%d (%s): did not "+
+				"return error on invalid index: %d - got: %v, "+
+				"want: non-nil", i, dbType, wantHeight, err)
+			return false
+		}
+		if hashFromDb != nil {
+			t.Errorf("FetchBlockShaByHeight #%d (%s): returned "+
+				"hash is not nil on invalid index: %d - got: "+
+				"%v, want: nil", i, dbType, wantHeight, err)
+			return false
+		}
+	}
+
+	return false
+}
+
 // testInterface tests performs tests for the various interfaces of btcdb which
 // require state in the database for the given database type.
 func testInterface(t *testing.T, dbType string) {
@@ -107,6 +131,11 @@ func testInterface(t *testing.T, dbType string) {
 		}
 	}
 
+	// Ensure FetchBlockShaByHeight handles invalid heights properly.
+	if !testFetchBlockShaByHeightErrors(t, dbType, db, int64(len(blocks))) {
+		return
+	}
+
 	// TODO(davec): Need to figure out how to handle the special checks
 	// required for the duplicate transactions allowed by blocks 91842 and
 	// 91880 on the main network due to the old miner + Satoshi client bug.
@@ -117,7 +146,7 @@ func testInterface(t *testing.T, dbType string) {
 	   DropAfterBlockBySha(*btcwire.ShaHash) (err error)
 	   - ExistsSha(sha *btcwire.ShaHash) (exists bool)
 	   - FetchBlockBySha(sha *btcwire.ShaHash) (blk *btcutil.Block, err error)
-	   FetchBlockShaByHeight(height int64) (sha *btcwire.ShaHash, err error)
+	   - FetchBlockShaByHeight(height int64) (sha *btcwire.ShaHash, err error)
 	   FetchHeightRange(startHeight, endHeight int64) (rshalist []btcwire.ShaHash, err error)
 	   ExistsTxSha(sha *btcwire.ShaHash) (exists bool)
 	   FetchTxBySha(txsha *btcwire.ShaHash) ([]*TxListReply, error)