diff --git a/test/emacs-subject-to-filename b/test/emacs-subject-to-filename
new file mode 100755
index 00000000..176e6859
--- /dev/null
+++ b/test/emacs-subject-to-filename
@@ -0,0 +1,138 @@
+#!/usr/bin/env bash
+
+test_description="emacs: mail subject to filename"
+. test-lib.sh
+
+# emacs server can't be started in a child process with $(test_emacs ...)
+test_emacs '(ignore)'
+
+# test notmuch-wash-subject-to-patch-sequence-number (subject)
+test_begin_subtest "no patch sequence number"
+output=$(test_emacs '(notmuch-wash-subject-to-patch-sequence-number
+      "[PATCH] A normal patch subject without numbers")'
+)
+test_expect_equal "$output" ""
+
+test_begin_subtest "patch sequence number #1"
+output=$(test_emacs '(notmuch-wash-subject-to-patch-sequence-number
+      "[PATCH 2/3] A most regular patch subject")'
+)
+test_expect_equal "$output" 2
+
+test_begin_subtest "patch sequence number #2"
+output=$(test_emacs '(notmuch-wash-subject-to-patch-sequence-number
+      "  [dummy list prefix]  [RFC PATCH v2 13/42]  Special prefixes")'
+)
+test_expect_equal "$output" 13
+
+test_begin_subtest "patch sequence number #3"
+output=$(test_emacs '(notmuch-wash-subject-to-patch-sequence-number
+      "[PATCH 2/3] [PATCH 032/037] use the last prefix")'
+)
+test_expect_equal "$output" 32
+
+test_begin_subtest "patch sequence number #4"
+output=$(test_emacs '(notmuch-wash-subject-to-patch-sequence-number
+      "[dummy list prefix] [PATCH 2/3] PATCH 3/3] do not use a broken prefix")'
+)
+test_expect_equal "$output" 2
+
+test_begin_subtest "patch sequence number #5"
+output=$(test_emacs '(notmuch-wash-subject-to-patch-sequence-number
+      "[RFC][PATCH 3/5][PATCH 4/5][PATCH 5/5] A made up test")'
+)
+test_expect_equal "$output" 5
+
+test_begin_subtest "patch sequence number #6"
+output=$(test_emacs '(notmuch-wash-subject-to-patch-sequence-number
+      "[PATCH 2/3] this -> [PATCH 3/3] is not a prefix anymore [nor this 4/4]")'
+)
+test_expect_equal "$output" 2
+
+test_begin_subtest "patch sequence number #7"
+output=$(test_emacs '(notmuch-wash-subject-to-patch-sequence-number
+      "[liberally accept crapola right before123/456and after] the numbers")'
+)
+test_expect_equal "$output" 123
+
+# test notmuch-wash-subject-to-filename (subject &optional maxlen)
+test_begin_subtest "filename #1"
+output=$(test_emacs '(notmuch-wash-subject-to-filename
+      "just a subject line")'
+)
+test_expect_equal $output '"just-a-subject-line"'
+
+test_begin_subtest "filename #2"
+output=$(test_emacs '(notmuch-wash-subject-to-filename
+      " [any]  [prefixes are ] [removed!] from the subject")'
+)
+test_expect_equal $output '"from-the-subject"'
+
+test_begin_subtest "filename #3"
+output=$(test_emacs '(notmuch-wash-subject-to-filename
+      "  leading and trailing space  ")'
+)
+test_expect_equal $output '"leading-and-trailing-space"'
+
+test_begin_subtest "filename #4"
+output=$(test_emacs '(notmuch-wash-subject-to-filename
+      "!#  leading ()// &%, and in between_and_trailing garbage ()(&%%")'
+)
+test_expect_equal $output '"-leading-and-in-between_and_trailing-garbage"'
+
+test_begin_subtest "filename #5"
+output=$(test_emacs '(notmuch-wash-subject-to-filename
+      "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz.-_01234567890")'
+)
+test_expect_equal $output '"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz.-_01234567890"'
+
+test_begin_subtest "filename #6"
+output=$(test_emacs '(notmuch-wash-subject-to-filename
+      "sequences of ... are squashed and trailing are removed ...")'
+)
+test_expect_equal $output '"sequences-of-.-are-squashed-and-trailing-are-removed"'
+
+test_begin_subtest "filename #7"
+output=$(test_emacs '(notmuch-wash-subject-to-filename
+      "max length test" 1)'
+)
+test_expect_equal $output '"m"'
+
+test_begin_subtest "filename #8"
+output=$(test_emacs '(notmuch-wash-subject-to-filename
+      "max length test /&(/%&/%%&¤%¤" 20)'
+)
+test_expect_equal $output '"max-length-test"'
+
+test_begin_subtest "filename #9"
+output=$(test_emacs '(notmuch-wash-subject-to-filename
+      "[a prefix] [is only separated] by [spaces], so \"by\" is not okay!")'
+)
+test_expect_equal $output '"by-spaces-so-by-is-not-okay"'
+
+# test notmuch-wash-subject-to-patch-filename (subject)
+test_begin_subtest "patch filename #1"
+output=$(test_emacs '(notmuch-wash-subject-to-patch-filename
+      "[RFC][PATCH 099/100] rewrite notmuch")'
+)
+test_expect_equal "$output" '"0099-rewrite-notmuch.patch"'
+
+test_begin_subtest "patch filename #2"
+output=$(test_emacs '(notmuch-wash-subject-to-patch-filename
+      "[RFC PATCH v1] has no patch number, default to 1")'
+)
+test_expect_equal "$output" '"0001-has-no-patch-number-default-to-1.patch"'
+
+test_begin_subtest "patch filename #3"
+output=$(test_emacs '(notmuch-wash-subject-to-patch-filename
+      "[PATCH 4/5] the maximum length of a patch filename is 52 + patch sequence number + .patch extension")'
+)
+test_expect_equal "$output" '"0004-the-maximum-length-of-a-patch-filename-is-52-patch-s.patch"'
+
+test_begin_subtest "patch filename #4"
+output=$(test_emacs '(notmuch-wash-subject-to-patch-filename
+      "[PATCH 4/5] the maximum length of a patch filename is 52 + patchh ! sequence number + .patch extension, *before* trimming trailing - and .")'
+)
+test_expect_equal "$output" '"0004-the-maximum-length-of-a-patch-filename-is-52-patchh.patch"'
+
+test_done
diff --git a/test/notmuch-test b/test/notmuch-test
index ded79e8f..e40ef86a 100755
--- a/test/notmuch-test
+++ b/test/notmuch-test
@@ -42,6 +42,7 @@ TESTS="
   encoding
   emacs
   emacs-large-search-buffer
+  emacs-subject-to-filename
   maildir-sync
   crypto
   symbol-hiding