Capture stdout/stderr during tests and display it for failures

test/fixtures/output.bats

@@ -0,0 +1,19 @@
+@test "success writing to stdout" {
+  echo "success stdout 1"
+  echo "success stdout 2"
+}
+
+@test "success writing to stderr" {
+  echo "success stderr" >&2
+}
+
+@test "failure writing to stdout" {
+  echo "failure stdout 1"
+  echo "failure stdout 2"
+  false
+}
+
+@test "failure writing to stderr" {
+  echo "failure stderr" >&2
+  false
+}