Add tests for which command

test/which_command.bats

@@ -0,0 +1,38 @@
+#!/usr/bin/env bats
+
+load test_helpers
+
+. $(dirname $BATS_TEST_DIRNAME)/lib/commands/which.sh
+. $(dirname $BATS_TEST_DIRNAME)/lib/commands/install.sh
+
+setup() {
+  setup_asdf_dir
+  install_dummy_plugin
+  run install_command dummy 1.0
+
+  PROJECT_DIR=$HOME/project
+  mkdir $PROJECT_DIR
+}
+
+teardown() {
+  clean_asdf_dir
+}
+
+@test "which should show dummy 1.0 main binary path" {
+  cd $PROJECT_DIR
+
+  echo 'dummy 1.0' >> $PROJECT_DIR/.tool-versions
+
+  run current_version "dummy"
+  [ "$output" = "1.0" ]
+
+  run which_command "dummy"
+  [ "$status" -eq 0 ]
+  [ "$output" = "$ASDF_DIR/installs/dummy/1.0/bin/dummy" ]
+}
+
+@test "which should error when the plugin doesn't exist" {
+  run which_command "foobar"
+  [ "$status" -eq 1 ]
+  [ "$output" = "No such plugin" ]
+}