diff --git a/test/add.bats b/test/add.bats
new file mode 100644
index 0000000..5a20d61
--- /dev/null
+++ b/test/add.bats
@@ -0,0 +1,112 @@
+#!/usr/bin/env bats
+
+load test_helper
+
+# `hosts add` #################################################################
+
+@test "\`add\` with no arguments exits with status 1." {
+  run "$_HOSTS" add
+  printf "\$status: %s\n" "$status"
+  printf "\$output: '%s'\n" "$output"
+  [[ $status -eq 1 ]]
+}
+
+@test "\`add\` with no argument does not change the hosts file." {
+  _original="$(cat "${HOSTS_PATH}")"
+
+  run "$_HOSTS" add
+  printf "\$status: %s\n" "$status"
+  printf "\$output: '%s'\n" "$output"
+  [[ "$(cat "${HOSTS_PATH}")" == "${_original}" ]]
+}
+
+@test "\`add\` with no arguments prints help information." {
+  run "$_HOSTS" add
+  printf "\$status: %s\n" "$status"
+  printf "\$output: '%s'\n" "$output"
+  [[ "${lines[0]}" == "Usage:" ]]
+  [[ "${lines[1]}" == "  hosts add <ip> <hostname> [comment]" ]]
+}
+
+# `hosts add <ip>` ############################################################
+
+@test "\`add <ip>\` exits with status 1." {
+  run "$_HOSTS" add 0.0.0.0
+  printf "\$status: %s\n" "$status"
+  printf "\$output: '%s'\n" "$output"
+  [[ $status -eq 1 ]]
+}
+
+@test "\`add <ip>\` does not change the hosts file." {
+  _original="$(cat "${HOSTS_PATH}")"
+
+  run "$_HOSTS" add 0.0.0.0
+  printf "\$status: %s\n" "$status"
+  printf "\$output: '%s'\n" "$output"
+  [[ "$(cat "${HOSTS_PATH}")" == "${_original}" ]]
+}
+
+@test "\`add <ip>\` prints help information." {
+  run "$_HOSTS" add 0.0.0.0
+  printf "\$status: %s\n" "$status"
+  printf "\$output: '%s'\n" "$output"
+  [[ "${lines[0]}" == "Please include a hostname" ]]
+  [[ "${lines[1]}" == "Usage:" ]]
+  [[ "${lines[2]}" == "  hosts add <ip> <hostname> [comment]" ]]
+}
+
+# `hosts add <ip> <hostname>` #################################################
+
+@test "\`add <ip> <hostname>\` exits with status 0." {
+  run "$_HOSTS" add 0.0.0.0 example.com
+  printf "\$status: %s\n" "$status"
+  printf "\$output: '%s'\n" "$output"
+  [[ $status -eq 0 ]]
+}
+
+@test "\`add <ip> <hostname>\` adds the entry to the hosts file." {
+  _original="$(cat "${HOSTS_PATH}")"
+
+  run "$_HOSTS" add 0.0.0.0 example.com
+  printf "\$status: %s\n" "$status"
+  printf "\$output: '%s'\n" "$output"
+  _compare "${_original}" "$(cat "${HOSTS_PATH}")"
+  _compare '0.0.0.0	example.com' "$(sed -n '11p' "${HOSTS_PATH}")"
+  [[ "$(cat "${HOSTS_PATH}")" != "${_original}" ]]
+  [[ "$(sed -n '11p' "${HOSTS_PATH}")" == "0.0.0.0	example.com" ]]
+}
+
+@test "\`add <ip> <hostname>\` prints feedback." {
+  run "$_HOSTS" add 0.0.0.0 example.com
+  printf "\$status: %s\n" "$status"
+  printf "\$output: '%s'\n" "$output"
+  [[ "${lines[0]}" == "Added:" ]]
+  [[ "${lines[1]}" == "0.0.0.0	example.com" ]]
+}
+
+# `hosts add <ip> <hostname> [comment]` #######################################
+
+@test "\`add <ip> <hostname> [comment]\` exits with status 0." {
+  run "$_HOSTS" add 0.0.0.0 example.com 'Comment.'
+  printf "\$status: %s\n" "$status"
+  printf "\$output: '%s'\n" "$output"
+  [[ $status -eq 0 ]]
+}
+
+@test "\`add <ip> <hostname> [comment]\` adds the entry to the hosts file." {
+  _original="$(cat "${HOSTS_PATH}")"
+
+  run "$_HOSTS" add 0.0.0.0 example.com 'Comment.'
+  printf "\$status: %s\n" "$status"
+  printf "\$output: '%s'\n" "$output"
+  [[ "$(cat "${HOSTS_PATH}")" != "${_original}" ]]
+  [[ "$(sed -n '11p' "${HOSTS_PATH}")" == "0.0.0.0	example.com	# Comment." ]]
+}
+
+@test "\`add <ip> <hostname> [comment]\` prints feedback." {
+  run "$_HOSTS" add 0.0.0.0 example.com 'Comment.'
+  printf "\$status: %s\n" "$status"
+  printf "\$output: '%s'\n" "$output"
+  [[ "${lines[0]}" == "Added:" ]]
+  [[ "${lines[1]}" == "0.0.0.0	example.com	# Comment." ]]
+}