[New] nvm use/nvm install: add --save option

Fixes #2849.

Co-authored-by: Martin <maartin00000@gmail.com>
Co-authored-by: Jordan Harband <ljharb@gmail.com>

test/fast/Unit tests/nvm_write_nvmrc

@@ -0,0 +1,86 @@
+#!/bin/sh
+\. ../../../nvm.sh
+\. ../../common.sh
+
+set -e
+
+TEST_VERSION="v0.2.4"
+
+if [ -f .nvmrc ]; then mv .nvmrc .nvmrc.orig; fi
+
+del_nvmrc () {
+  rm -f .nvmrc
+}
+
+del_alias () {
+  nvm unalias test >/dev/null 2>&1
+}
+
+cleanup () {
+  del_nvmrc
+  del_alias
+  nvm cache clear
+  nvm deactivate
+  nvm unalias default
+  rm -rf ${NVM_DIR}/v*
+  if [ -f .nvmrc.orig ]; then mv .nvmrc.orig .nvmrc; fi
+  unset -f nvm_ls_remote nvm_ls_remote_iojs
+}
+
+die () {
+  echo "$@"
+  cleanup
+  exit 1
+}
+
+REMOTE="$PWD/mocks/nvm_ls_remote.txt"
+nvm_ls_remote() {
+  cat "$REMOTE"
+}
+REMOTE_IOJS="$PWD/mocks/nvm_ls_remote_iojs.txt"
+nvm_ls_remote_iojs() {
+  cat "$REMOTE_IOJS"
+}
+
+make_fake_node "$TEST_VERSION"
+
+test_version () {
+  del_nvmrc
+  VERSION_STRING=${1-}
+  make_fake_node "$VERSION_STRING"
+
+  nvm_write_nvmrc $VERSION_STRING || die "\`nvm_write_nvmrc ${VERSION_STRING}\` failed"
+  OUTPUT="$(cat .nvmrc)"
+
+  nvm_is_valid_version "$(cat .nvmrc)" \
+    || die "\`nvm install --save ${VERSION_STRING}\`+ \`cat .nvmrc\` outputted invalid version: got '${OUTPUT}'"
+}
+
+# 1.
+
+test_version "$TEST_VERSION" || die
+
+# 2. with an alias
+del_alias
+nvm alias test "$TEST_VERSION"
+test_version test || die
+
+# 3. fails with invalid permissions
+del_nvmrc
+touch .nvmrc
+chmod 0 .nvmrc
+nvm_write_nvmrc $TEST_VERSION 2>/dev/null && die "\`nvm_write_nvmrc $TEST_VERSION\` did not fail with invalid permissions"
+del_nvmrc
+
+# 4. respects NVM_SILENT=1
+export NVM_SILENT=1
+[ "$(nvm_write_nvmrc $TEST_VERSION)" = "" ] || die "\`nvm_write_nvmrc $TEST_VERSION\` was not silenced by NVM_SILENT=1"
+unset NVM_SILENT
+
+# 5. fails with an invalid version number
+TEST_VERSION="not_a_node_version"
+nvm_write_nvmrc $TEST_VERSION 2>/dev/null && die "\`nvm_write_nvmrc $TEST_VERSION\` did not fail"
+
+#
+
+cleanup