Make asynchronous suggestions disabled by default

While they are still experimental

spec/options/async_zpty_name_spec.rb

@@ -1,15 +1,19 @@
-describe 'the zpty for async suggestions' do
-  it 'is created with the default name' do
-    session.run_command('zpty -t zsh_autosuggest_pty &>/dev/null; echo $?')
-    wait_for { session.content }.to end_with("\n0")
-  end
+context 'when async suggestions are enabled' do
+  let(:options) { ["ZSH_AUTOSUGGEST_USE_ASYNC="] }
 
-  context 'when ZSH_AUTOSUGGEST_ASYNC_PTY_NAME is set' do
-    let(:options) { ['ZSH_AUTOSUGGEST_ASYNC_PTY_NAME=foo_pty'] }
-
-    it 'is created with the specified name' do
-      session.run_command('zpty -t foo_pty &>/dev/null; echo $?')
+  describe 'the zpty for async suggestions' do
+    it 'is created with the default name' do
+      session.run_command('zpty -t zsh_autosuggest_pty &>/dev/null; echo $?')
       wait_for { session.content }.to end_with("\n0")
     end
+
+    context 'when ZSH_AUTOSUGGEST_ASYNC_PTY_NAME is set' do
+      let(:options) { super() + ['ZSH_AUTOSUGGEST_ASYNC_PTY_NAME=foo_pty'] }
+
+      it 'is created with the specified name' do
+        session.run_command('zpty -t foo_pty &>/dev/null; echo $?')
+        wait_for { session.content }.to end_with("\n0")
+      end
+    end
   end
 end

spec/options/use_async_spec.rb

@@ -1,7 +1,7 @@
 describe 'suggestion fetching' do
-  it 'is performed asynchronously'
+  it 'is performed synchronously'
 
-  context 'when ZSH_AUTOSUGGEST_USE_ASYNC is unset' do
-    it 'is performed synchronously'
+  context 'when ZSH_AUTOSUGGEST_USE_ASYNC is set' do
+    it 'is performed asynchronously'
   end
 end