diff --git a/.gitmodules b/.gitmodules
new file mode 100644
index 0000000..a0406d6
--- /dev/null
+++ b/.gitmodules
@@ -0,0 +1,9 @@
+[submodule "shell/test/bats"]
+	path = shell/test/bats
+	url = https://github.com/bats-core/bats-core.git
+[submodule "shell/test/test_helper/bats-support"]
+	path = shell/test/test_helper/bats-support
+	url = https://github.com/bats-core/bats-support.git
+[submodule "shell/test/test_helper/bats-assert"]
+	path = shell/test/test_helper/bats-assert
+	url = https://github.com/bats-core/bats-assert.git
diff --git a/shell/next.sh b/shell/next.sh
index 35cd496..c2d0f96 100755
--- a/shell/next.sh
+++ b/shell/next.sh
@@ -37,6 +37,13 @@ if [ $2 ]; then
     fi
 fi
 
-# HACK: emacs won't accept piped input as a file name, so we use --eval to open
-# the file via find-file.
-emacsclient --eval "(progn (find-file \"$NEXTFILE\") (um-journal-header) $UMTAG (message \"creating $NEXTFILE\"))"
+UMELISP="(progn (find-file \"$NEXTFILE\") (um-journal-header) $UMTAG (message \"creating $NEXTFILE\"))"
+
+# for testing and piping
+if [ $UMNEXTECHO = true ]; then
+    echo $NEXTFILE $UMTAG
+else
+    # HACK: emacs won't accept piped input as a file name, so we use --eval to open
+    # the file via find-file.
+    emacsclient --eval "$UMELISP"
+fi
diff --git a/shell/test/bats b/shell/test/bats
new file mode 160000
index 0000000..3d3f63d
--- /dev/null
+++ b/shell/test/bats
@@ -0,0 +1 @@
+Subproject commit 3d3f63d9772b98c88586ec0a66bd358a85d9b4a6
diff --git a/shell/test/001.md b/shell/test/mockjournal/001.md
similarity index 100%
rename from shell/test/001.md
rename to shell/test/mockjournal/001.md
diff --git a/shell/test/002.blah.md b/shell/test/mockjournal/002.blah.md
similarity index 100%
rename from shell/test/002.blah.md
rename to shell/test/mockjournal/002.blah.md
diff --git a/shell/test/004.foo.md b/shell/test/mockjournal/004.foo.md
similarity index 100%
rename from shell/test/004.foo.md
rename to shell/test/mockjournal/004.foo.md
diff --git a/shell/test/005.md b/shell/test/mockjournal/005.md
similarity index 100%
rename from shell/test/005.md
rename to shell/test/mockjournal/005.md
diff --git a/shell/test/009.boo.md b/shell/test/mockjournal/009.boo.md
similarity index 100%
rename from shell/test/009.boo.md
rename to shell/test/mockjournal/009.boo.md
diff --git a/shell/test/098.baa.md b/shell/test/mockjournal/098.baa.md
similarity index 100%
rename from shell/test/098.baa.md
rename to shell/test/mockjournal/098.baa.md
diff --git a/shell/test/099.poo.md b/shell/test/mockjournal/099.poo.md
similarity index 100%
rename from shell/test/099.poo.md
rename to shell/test/mockjournal/099.poo.md
diff --git a/shell/test/test_helper/bats-assert b/shell/test/test_helper/bats-assert
new file mode 160000
index 0000000..e2d855b
--- /dev/null
+++ b/shell/test/test_helper/bats-assert
@@ -0,0 +1 @@
+Subproject commit e2d855bc78619ee15b0c702b5c30fb074101159f
diff --git a/shell/test/test_helper/bats-support b/shell/test/test_helper/bats-support
new file mode 160000
index 0000000..9bf10e8
--- /dev/null
+++ b/shell/test/test_helper/bats-support
@@ -0,0 +1 @@
+Subproject commit 9bf10e876dd6b624fe44423f0b35e064225f7556
diff --git a/shell/test/um.bats b/shell/test/um.bats
new file mode 100644
index 0000000..234bbde
--- /dev/null
+++ b/shell/test/um.bats
@@ -0,0 +1,82 @@
+setup() {
+    load 'test_helper/bats-support/load'
+    load 'test_helper/bats-assert/load'
+
+    # get the containing directory of this file
+    # use $BATS_TEST_FILENAME instead of ${BASH_SOURCE[0]} or $0,
+    # as those will point to the bats executable's location or the preprocessed file respectively
+    DIR="$( cd "$( dirname "$BATS_TEST_FILENAME" )" >/dev/null 2>&1 && pwd )"
+    # make executables visible to PATH
+    PATH="$DIR/..:$PATH"
+    # commands depend on being in the journal/ path.
+    cd $DIR/mockjournal
+    # so that we can run next.sh without dealing with emacsclient.
+    export UMNEXTECHO=true
+}
+
+teardown() {
+    export UMNEXTECHO=false
+    cd -
+}
+
+@test "um usage" {
+    run um
+    assert_output 'usage: um (next|last|cat|rename|tag)'
+}
+
+@test "next empty" {
+    run um next
+    assert_output '100.md'
+}
+
+@test "next descriptor" {
+    run um next foo
+    assert_output '100.foo.md'
+}
+
+@test "next descriptor tag" {
+    run um next foo bar
+    assert_output --partial '(insert "+ bar\n")'
+}
+
+@test "next descriptor +" {
+    run um next foo +
+    assert_output --partial '(insert "+ foo\n")'
+}
+
+@test "um last" {
+    run um last
+    assert_output '099.poo.md'
+}
+
+@test "um cat" {
+    run um cat 001.md 002.blah.md
+    assert_output '# 001
+: 2024.01.14
++ foo
+
+---
+
+# 002.blah
+: 2024.01.14
++ foo'
+}
+
+um_rename_awk() {
+    echo "$1
+$2" | awk -f ../../rename.awk
+}
+
+@test "rename.awk" {
+    run um_rename_awk 01.md foo
+    assert_output '01.md 01.foo.md'
+
+    run um_rename_awk 01.foo.md bar
+    assert_output '01.foo.md 01.bar.md'
+}
+
+@test "um tag" {
+    run um tag foo
+    assert_output '001.md
+002.blah.md'
+}