assertions: Fix failure output handling

The `fail` and `assert_line_matches` calls to `printf` were
interpolating the `output` string into the format string argument, which
meant `printf` got confused when those strings contained `%` characters.
This tests for and fixes the bug in each location, and also sets all
`printf` format strings to use single-quotes.

Author: mbland

tests/assertions.bash

@@ -22,7 +22,7 @@ __return_from_bats_assertion() {
 
 fail() {
   set +o functrace
-  printf "STATUS: ${status}\nOUTPUT:\n${output}\n" >&2
+  printf 'STATUS: %s\nOUTPUT:\n%s\n' "$status" "$output" >&2
   __return_from_bats_assertion 1
 }
 
@@ -33,7 +33,7 @@ assert_equal() {
   local label="$3"
 
   if [[ "$expected" != "$actual" ]]; then
-    printf "%s not equal to expected value:\n  %s\n  %s\n" \
+    printf '%s not equal to expected value:\n  %s\n  %s\n' \
       "$label" "expected: '$expected'" "actual:   '$actual'" >&2
     __return_from_bats_assertion 1
   else
@@ -48,7 +48,7 @@ assert_matches() {
   local label="$3"
 
   if [[ ! "$value" =~ $pattern ]]; then
-    printf "%s does not match expected pattern:\n  %s\n  %s\n" \
+    printf '%s does not match expected pattern:\n  %s\n  %s\n' \
       "$label" "pattern: '$pattern'" "value:   '$value'" >&2
     __return_from_bats_assertion 1
   else
@@ -116,7 +116,7 @@ __assert_line() {
   fi
 
   if ! "$assertion" "$constraint" "${lines[$lineno]}" "line $lineno"; then
-    printf "OUTPUT:\n$output\n" >&2
+    printf 'OUTPUT:\n%s\n' "$output" >&2
     __return_from_bats_assertion 1
   else
     __return_from_bats_assertion

tests/assertions.bats

@@ -110,6 +110,14 @@ check_expected_output() {
     'Hello, world!'
 }
 
+@test "$SUITE: fail handles strings containing percentage signs" {
+  expect_failure "echo '% not interpreted as a format spec'" \
+    'fail' \
+    'STATUS: 0' \
+    'OUTPUT:' \
+    '% not interpreted as a format spec'
+}
+
 @test "$SUITE: assert_equal success" {
   expect_success "echo 'Hello, world!'" \
     'assert_equal "Hello, world!" "$output" "echo result"'
@@ -291,3 +299,13 @@ check_expected_output() {
     'OUTPUT:' \
     'Hello, world!'
 }
+
+@test "$SUITE: assert_line_matches failure handles percent signs in output" {
+  expect_failure "echo '% not interpreted as a format spec'" \
+    "assert_line_matches 0 '% interpreted as a format spec'" \
+    'line 0 does not match expected pattern:' \
+    "  pattern: '% interpreted as a format spec'" \
+    "  value:   '% not interpreted as a format spec'" \
+    'OUTPUT:' \
+    '% not interpreted as a format spec'
+}