default to 'python' when not running test suite

test/test_interactive.sh

@@ -1,5 +1,7 @@
 #!/usr/bin/env bash
 
+[ -z "${BETEXC_PYTHON}" ] && export BETEXC_PYTHON=python
+
 /usr/bin/expect -f - <<EOF
 spawn ${BETEXC_PYTHON} -m better_exceptions -q
 expect ">>> "

test/test_interactive_raw.sh

@@ -1,5 +1,7 @@
 #!/usr/bin/env bash
 
+[ -z "${BETEXC_PYTHON}" ] && export BETEXC_PYTHON=python
+
 /usr/bin/expect -f - <<EOF
 spawn ${BETEXC_PYTHON} -m test_util.quiet_console
 expect ">>> "

test/test_string.sh

@@ -1,6 +1,8 @@
 #!/usr/bin/env bash
 set -e
 
+[ -z "${BETEXC_PYTHON}" ] && export BETEXC_PYTHON=python
+
 TEST_STR='import better_exceptions; a = 5; assert a > 10'
 
 "${BETEXC_PYTHON}" -c "${TEST_STR}"