Add rbenv-install tests

test/rbenv.bats

+#!/usr/bin/env bats
+
+load test_helper
+export RBENV_ROOT="${TMP}/rbenv"
+
+setup() {
+  stub rbenv-hooks 'install : true'
+  stub rbenv-rehash 'true'
+}
+
+stub_ruby_build() {
+  stub ruby-build "--lib : $BATS_TEST_DIRNAME/../bin/ruby-build --lib" "$@"
+}
+
+@test "install proper" {
+  stub_ruby_build 'echo ruby-build "$@"'
+
+  run rbenv-install 2.1.2
+  assert_success "ruby-build 2.1.2 ${RBENV_ROOT}/versions/2.1.2"
+
+  unstub ruby-build
+  unstub rbenv-hooks
+  unstub rbenv-rehash
+}
+
+@test "install rbenv local version by default" {
+  stub_ruby_build 'echo ruby-build "$1"'
+  stub rbenv-local 'echo 2.1.2'
+
+  run rbenv-install
+  assert_success "ruby-build 2.1.2"
+
+  unstub ruby-build
+  unstub rbenv-local
+}
+
+@test "list available versions" {
+  stub_ruby_build \
+    "--definitions : echo 1.8.7 1.9.3-p0 1.9.3-p194 2.1.2 | tr ' ' $'\\n'"
+
+  run rbenv-install --list
+  assert_success
+  assert_output <<OUT
+Available versions:
+  1.8.7
+  1.9.3-p0
+  1.9.3-p194
+  2.1.2
+OUT
+
+  unstub ruby-build
+}
+
+@test "nonexistent version" {
+  stub_ruby_build 'echo ERROR >&2 && exit 2' \
+    "--definitions : echo 1.8.7 1.9.3-p0 1.9.3-p194 2.1.2 | tr ' ' $'\\n'"
+
+  run rbenv-install 1.9.3
+  assert_failure
+  assert_output <<OUT
+ERROR
+
+The following versions contain \`1.9.3' in the name:
+  1.9.3-p0
+  1.9.3-p194
+
+You can list all available versions with \`rbenv install --list'.
+
+If the version you're looking for is not present, first try upgrading
+ruby-build. If it's still missing, open a request on the ruby-build
+issue tracker: https://github.com/sstephenson/ruby-build/issues
+OUT
+
+  unstub ruby-build
+}