Add tests styleguide

Author: rubiojr

test/README.md

@@ -0,0 +1,37 @@
+--
+### Writing tests
+
+See also the [Bash style guide](../README.md)
+
+--
+##### all tests should use `set -e` and call `setup` before making any assertions
+
+Like this:
+
+```bash
+begin_test "echo works"
+(
+  set -e
+  setup
+
+  echo passing | grep passing
+)
+end_test
+```
+
+--
+##### Resist the urge to disable `set -e`
+
+If you want to assert failure, please resist the urge to disable `set -e` and
+instead use negation with `!`:
+
+```bash
+begin_test "netcat is not from bsd"
+(
+  set -e
+  setup
+
+  ! nc -h 2>&1 | grep bsd
+)
+end_test
+```