[[ isn't a simple command and thus isn't subject to set -e

test/bats.bats

@@ -4,25 +4,25 @@ FIXTURE_ROOT="$BATS_TEST_DIRNAME/fixtures"
 
 @test "no arguments prints usage instructions" {
   run bats
-  [[ $status -eq 1 ]]
-  [[ $output =~ ^usage: ]]
+  [ $status -eq 1 ]
+  [ $(expr "$output" : "usage:") -ne 0 ]
 }
 
 @test "invalid filename prints an error" {
   run bats nonexistent
-  [[ $status -eq 1 ]]
-  [[ $output =~ does\ not\ exist ]]
+  [ $status -eq 1 ]
+  [ $(expr "$output" : ".*does not exist") -ne 0 ]
 }
 
 @test "empty test file runs zero tests" {
   run bats "$FIXTURE_ROOT/empty.bats"
-  [[ $status -eq 0 ]]
-  [[ $output = "1..0" ]]
+  [ $status -eq 0 ]
+  [ $output = "1..0" ]
 }
 
 @test "one passing test" {
   run bats "$FIXTURE_ROOT/one_passing.bats"
-  [[ $status -eq 0 ]]
-  [[ ${lines[0]} = "1..1" ]]
-  [[ ${lines[1]} = "ok 1 a passing test" ]]
+  [ $status -eq 0 ]
+  [ ${lines[0]} = "1..1" ]
+  [ ${lines[1]} = "ok 1 a passing test" ]
 }