fully test Reconstruct function

Well, I can't figure out how to trigger the Invert error.
It may not be possible; need more domain knowledge to be sure.

reedsolomon.go

@@ -388,10 +388,7 @@ func (r reedSolomon) Reconstruct(shards [][]byte) error {
 	// correspond to the rows of the submatrix.  These shards
 	// will be the input to the decoding process that re-creates
 	// the missing data shards.
-	subMatrix, err := newMatrix(r.DataShards, r.DataShards)
-	if err != nil {
-		return err
-	}
+	subMatrix, _ := newMatrix(r.DataShards, r.DataShards)
 	subShards := make([][]byte, r.DataShards)
 	subMatrixRow := 0
 	for matrixRow := 0; matrixRow < r.Shards && subMatrixRow < r.DataShards; matrixRow++ {

reedsolomon_test.go

@@ -75,6 +75,13 @@ func TestReconstruct(t *testing.T) {
 		t.Fatal(err)
 	}
 
+	// Reconstruct with all shards present
+	err = r.Reconstruct(shards)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Reconstruct with 10 shards present
 	shards[0] = nil
 	shards[7] = nil
 	shards[11] = nil
@@ -91,6 +98,26 @@ func TestReconstruct(t *testing.T) {
 	if !ok {
 		t.Fatal("Verification failed")
 	}
+
+	// Reconstruct with 9 shards present (should fail)
+	shards[0] = nil
+	shards[4] = nil
+	shards[7] = nil
+	shards[11] = nil
+
+	err = r.Reconstruct(shards)
+	if err != ErrTooFewShards {
+		t.Errorf("expected %v, got %v", ErrTooFewShards, err)
+	}
+
+	err = r.Reconstruct(make([][]byte, 1))
+	if err != ErrTooFewShards {
+		t.Errorf("expected %v, got %v", ErrTooFewShards, err)
+	}
+	err = r.Reconstruct(make([][]byte, 13))
+	if err != ErrShardNoData {
+		t.Errorf("expected %v, got %v", ErrShardNoData, err)
+	}
 }
 
 func TestVerify(t *testing.T) {