Auto-resolve prefixes to the latest version (#2487)

test/latest.bats

@@ -0,0 +1,80 @@
+#!/usr/bin/env bats
+
+load test_helper
+
+setup() {
+  export PATH="${PYENV_TEST_DIR}/bin:$PATH"
+}
+
+create_executable() {
+  local name="$1"
+  local bin="${PYENV_TEST_DIR}/bin"
+  mkdir -p "$bin"
+  sed -Ee '1s/^ +//' > "${bin}/$name"
+  chmod +x "${bin}/$name"
+}
+
+@test "read from installed" {
+  create_executable pyenv-versions <<!
+#!$BASH
+echo 4.5.6
+!
+  run pyenv-latest 4
+  assert_success
+  assert_output <<!
+4.5.6
+!
+}
+
+@test "read from known" {
+  create_executable python-build <<!
+#!$BASH
+echo 4.5.6
+!
+  run pyenv-latest -k 4
+  assert_success
+  assert_output <<!
+4.5.6
+!
+}
+
+@test "installed version not found" {
+  create_executable pyenv-versions <<!
+#!$BASH
+echo 3.5.6
+echo 3.10.8
+!
+  run pyenv-latest 3.8
+  assert_failure
+  assert_output <<!
+pyenv: no installed versions match the prefix \`3.8'
+!
+}
+
+@test "known version not found" {
+  create_executable python-build <<!
+#!$BASH
+echo 3.5.6
+echo 3.10.8
+!
+  run pyenv-latest -k 3.8
+  assert_failure
+  assert_output <<!
+pyenv: no known versions match the prefix \`3.8'
+!
+}
+
+@test "sort CPython" {
+  create_executable pyenv-versions <<!
+#!$BASH
+echo 2.7.18
+echo 3.5.6
+echo 3.10.8
+echo 3.10.6
+!
+  run pyenv-latest 3
+  assert_success
+  assert_output <<!
+3.10.8
+!
+}