Add unittest

test/installer.bats

@@ -0,0 +1,45 @@
+#!/usr/bin/env bats
+
+load test_helper
+
+@test "installs pyenv-virtualenv into PREFIX" {
+  cd "$TMP"
+  PREFIX="${PWD}/usr" run "${BATS_TEST_DIRNAME}/../install.sh"
+  assert_success ""
+
+  cd usr
+
+  assert [ -x bin/pyenv-sh-activate ]
+  assert [ -x bin/pyenv-sh-deactivate ]
+  assert [ -x bin/pyenv-virtualenv ]
+  assert [ -x bin/pyenv-virtualenv-prefix ]
+  assert [ -x bin/pyenv-virtualenvs ]
+}
+
+@test "overwrites old installation" {
+  cd "$TMP"
+  mkdir -p bin
+  touch bin/pyenv-virtualenv
+
+  PREFIX="$PWD" run "${BATS_TEST_DIRNAME}/../install.sh"
+  assert_success ""
+
+  assert [ -x bin/pyenv-virtualenv ]
+  run grep "virtualenv" bin/pyenv-virtualenv
+  assert_success
+}
+
+@test "unrelated files are untouched" {
+  cd "$TMP"
+  mkdir -p bin share/bananas
+  chmod g-w bin
+  touch bin/bananas
+
+  PREFIX="$PWD" run "${BATS_TEST_DIRNAME}/../install.sh"
+  assert_success ""
+
+  assert [ -e bin/bananas ]
+
+  run ls -ld bin
+  assert_equal "r-x" "${output:4:3}"
+}