feat(util:testutil) add NewBlockOrFail(t, data) factory method

for use in tests

util/testutil/blocks.go

+package testutil
+
+import (
+	"testing"
+
+	blocks "github.com/jbenet/go-ipfs/blocks"
+)
+
+// NewBlockOrFail returns a block created from msgData. Signals test failure if
+// creation fails.
+//
+// NB: NewBlockOrFail accepts a msgData parameter to avoid non-determinism in
+// tests. Generating random block data could potentially result in unexpected
+// behavior in tests. Thus, it is left up to the caller to select the msgData
+// that will determine the blocks key.
+func NewBlockOrFail(t *testing.T, msgData string) blocks.Block {
+	block, blockCreationErr := blocks.NewBlock([]byte(msgData))
+	if blockCreationErr != nil {
+		t.Fatal(blockCreationErr)
+	}
+	return *block
+}