Add some very simple tests

.gitignore

@@ -1,2 +1 @@
-tests
 .*/

.travis.yml

@@ -8,8 +8,16 @@ services:
 before_install:
  - docker pull koalaman/shellcheck:latest
 
+jobs:
+  include:
+    - stage: test
+      script:
+      - docker run -v $(pwd):/scripts --workdir=/scripts koalaman/shellcheck:latest $(grep -lE '^#!/.+(ba)?sh$' $(git ls-files))
+    -
+      script:
+      - docker build -t ebooktools/scripts:latest .
+      - docker run ebooktools/scripts:latest tests/run.sh
 script:
- - docker run -v $(pwd):/scripts --workdir=/scripts koalaman/shellcheck:latest $(grep -lE '^#!/.+(ba)?sh$' $(git ls-files))
 
 matrix:
   fast_finish: true

tests/run.sh

@@ -0,0 +1,63 @@
+#!/usr/bin/env bash
+
+set -eEuo pipefail
+
+DIR=$(dirname "$(realpath "${BASH_SOURCE[0]}")")
+EXIT_CODE=0
+
+# shellcheck source=./lib.sh
+. "$DIR/../lib.sh"
+
+assert_eq() {
+	local expected="$1" got="$2" exit_immediately="${3:-false}"
+	echo -n "[line $(caller)] "
+	if [[ "$expected" != "$got" ]]; then
+		echo "ERROR: expected '$expected' but got '$got'"
+		EXIT_CODE=11
+		if [[ "$exit_immediately" == "true" ]]; then
+			exit "$EXIT_CODE"
+		fi
+	else
+		echo "OK"
+	fi
+}
+
+expect_err() {
+	local expr_to_eval="$1" exit_immediately="${2:-false}"
+	echo -n "[line $(caller)] "
+	if [[ "$($expr_to_eval >/dev/null 2>&1 && echo success)" != "" ]]; then
+		echo "ERROR: expected error for expression '$expr_to_eval'"
+		EXIT_CODE=12
+		if [[ "$exit_immediately" == "true" ]]; then
+			exit "$EXIT_CODE"
+		fi
+	else
+		echo "OK"
+	fi
+}
+
+# Test to_lower
+assert_eq "lower" "$(echo 'lower' | to_lower)"
+assert_eq "upper" "$(echo 'UPPER' | to_lower)"
+assert_eq "utf-8 кирилица" "$(echo 'UTF-8 КИРИЛИЦА' | to_lower)"
+
+# Test uniq_no_sort
+assert_eq '' "$(echo -n | uniq_no_sort)"
+assert_eq 'no newline' "$(echo -n 'no newline' | uniq_no_sort)"
+assert_eq \
+	$'zzz\naaa\nbbb' \
+	"$(echo $'zzz\nzzz\naaa\nzzz\naaa\nbbb\nbbb' | uniq_no_sort)"
+
+# Test str_concat
+expect_err 'str_concat' # The function needs at least 1 argument
+assert_eq "testmest123" "$(str_concat "" test mest 123)"
+assert_eq $'aa\nbb' "$(str_concat $'\n' aa bb)"
+
+# Test find_isbns
+assert_eq "" "$(echo -n | find_isbns)"
+assert_eq "" "$(echo "invalid isbn 1122334455" | find_isbns)"
+assert_eq "076532637X" "$(echo "just an isbn 076532637X in some text" | find_isbns)"
+assert_eq "075640407X,9780756404079" "$(echo "075640407X (ISBN13: 9780756404079)" | find_isbns)"
+assert_eq "9781610391849,1610391845" "$(echo "crazy!978-16–103⁻918 49 16 10—39¯1845-z" | find_isbns)"
+
+exit "$EXIT_CODE"