tarsum: name collision fix

If a tar were constructed with duplicate file names, then depending on
the order, it could result in same tarsum.

Signed-off-by: Vincent Batts <vbatts@redhat.com>

tarsum/fileinfosums_test.go

@@ -0,0 +1,45 @@
+package tarsum
+
+import "testing"
+
+func newFileInfoSums() FileInfoSums {
+	return FileInfoSums{
+		fileInfoSum{name: "file3", sum: "2abcdef1234567890", pos: 2},
+		fileInfoSum{name: "dup1", sum: "deadbeef1", pos: 5},
+		fileInfoSum{name: "file1", sum: "0abcdef1234567890", pos: 0},
+		fileInfoSum{name: "file4", sum: "3abcdef1234567890", pos: 3},
+		fileInfoSum{name: "dup1", sum: "deadbeef0", pos: 4},
+		fileInfoSum{name: "file2", sum: "1abcdef1234567890", pos: 1},
+	}
+}
+
+func TestSortFileInfoSums(t *testing.T) {
+	dups := newFileInfoSums().GetAllFile("dup1")
+	if len(dups) != 2 {
+		t.Errorf("expected length 2, got %d", len(dups))
+	}
+	dups.SortByNames()
+	if dups[0].Pos() != 4 {
+		t.Errorf("sorted dups should be ordered by position. Expected 4, got %d", dups[0].Pos())
+	}
+
+	fis := newFileInfoSums()
+	expected := "0abcdef1234567890"
+	fis.SortBySums()
+	got := fis[0].Sum()
+	if got != expected {
+		t.Errorf("Expected %q, got %q", expected, got)
+	}
+
+	fis = newFileInfoSums()
+	expected = "dup1"
+	fis.SortByNames()
+	gotFis := fis[0]
+	if gotFis.Name() != expected {
+		t.Errorf("Expected %q, got %q", expected, gotFis.Name())
+	}
+	// since a duplicate is first, ensure it is ordered first by position too
+	if gotFis.Pos() != 4 {
+		t.Errorf("Expected %d, got %d", 4, gotFis.Pos())
+	}
+}