test_cmp expect actual
'
+cat >expect <<'EOF'
+Subject: [PREFIX 1/1] header with . in it
+EOF
+test_expect_success 'subject prefixes have space prepended' '
+ git format-patch -n -1 --stdout --subject-prefix=PREFIX >patch &&
+ grep ^Subject: patch >actual &&
+ test_cmp expect actual
+'
+
+cat >expect <<'EOF'
+Subject: [1/1] header with . in it
+EOF
+test_expect_success 'empty subject prefix does not have extra space' '
+ git format-patch -n -1 --stdout --subject-prefix= >patch &&
+ grep ^Subject: patch >actual &&
+ test_cmp expect actual
+'
+
test_done