Initial test framework and first test.

Add a basic test framework, borrowed from the framework used
by git.git.  A shell script library (tests/test-lib.sh) helps
generate the fixtures, and simplifies the process of writing
test scripts.  Tests can be run as a suite (via 'make test')
or individually (sh tests/t0000-config.sh).  Results are aggregated
upon completion.  Includes a detailed README.

A basic test of config file processing is part of this commit.

Signed-off-by: Emil Sit <sit@emilsit.net>

tests/t0000-config.sh

@@ -0,0 +1,61 @@
+#!/bin/sh
+
+test_description='todo.sh configuration file location
+
+This test just makes sure that todo.sh can find its
+config files in the default locations and take arguments
+to find it somewhere else.
+'
+. ./test-lib.sh
+
+# Remove the pre-created todo.cfg to test behavior in its absence
+rm -f todo.cfg
+echo "Fatal error:  Cannot read configuration file $HOME/todo.cfg" > expect
+test_expect_success 'no config file' '
+    todo.sh > output 2>&1 || test_cmp expect output
+'
+
+# All the below tests will output the usage message.
+cat > expect << EOF
+Usage: todo.sh [-fhpantvV] [-d todo_config] action [task_number] [task_description]
+Try 'todo.sh -h' for more information.
+EOF
+
+cat > test.cfg << EOF
+export TODO_DIR=.
+export TODO_FILE="$TODO_DIR/todo.txt"
+export DONE_FILE="$TODO_DIR/done.txt"
+export REPORT_FILE="$TODO_DIR/report.txt"
+export TMP_FILE="$TODO_DIR/todo.tmp"
+touch used_config
+EOF
+
+rm -f used_config
+test_expect_success 'config file (default location 1)' '
+    cp test.cfg todo.cfg
+    todo.sh > output;
+    test_cmp expect output && test -f used_config &&
+        rm -f todo.cfg
+'
+
+rm -f used_config
+test_expect_success 'config file (default location 2)' '
+    cp test.cfg .todo.cfg
+    todo.sh > output;
+    test_cmp expect output && test -f used_config &&
+        rm -f .todo.cfg
+'
+
+rm -f used_config
+test_expect_success 'config file (command line)' '
+    todo.sh -d test.cfg > output;
+    test_cmp expect output && test -f used_config
+'
+
+rm -f used_config
+test_expect_success 'config file (env variable)' '
+    TODOTXT_CFG_FILE=test.cfg todo.sh > output;
+    test_cmp expect output && test -f used_config
+'
+
+test_done