You can now stub responses via Aws.config and client constructors.

aws-sdk-core/lib/aws-sdk-core/client_stubs.rb

@@ -12,26 +12,58 @@ def initialize(*args)
       @stubs = {}
       @stub_mutex = Mutex.new
       super
+      if Hash === @config.stub_responses
+        @config.stub_responses.each do |operation_name, stubs|
+          apply_stubs(operation_name, Array === stubs ? stubs : [stubs])
+        end
+        @config.stub_responses = true
+      end
     end
 
     # Configures what data / errors should be returned from the named operation
     # when response stubbing is enabled.
     #
     # ## Basic usage
     #
-    # By default, fake responses are generated. You can override the default
-    # fake data with specific response data by passing a hash.
+    # When you enable response stubbing, the client will generate fake
+    # responses and will not make any HTTP requests.
     #
-    #     # enable response stubbing in the client constructor
     #     client = Aws::S3::Client.new(stub_responses: true)
+    #     client.list_buckets
+    #     #=> #<struct Aws::S3::Types::ListBucketsOutput buckets=[], owner=nil>
     #
-    #     # specify the response data for #list_buckets
-    #     client.stub_responses(:list_buckets, buckets:[{name:'aws-sdk'}])
+    # You can provide stub data that will be returned by the client.
+    #
+    #     # stub data in the constructor
+    #     client = Aws::S3::Client.new(stub_responses: {
+    #       list_buckets: { bukets: [{name: 'my-bucket' }] },
+    #       get_object: { body: 'data' },
+    #     })
     #
-    #     # no api calls made, stub returned
-    #     client.list_buckets.map(&:name)
+    #     client.list_buckets.buckets.map(&:name) #=> ['my-bucket']
+    #     client.get_object(bucket:'name', key:'key').body.read #=> 'data'
+    #
+    # You can also specify the stub data using {#stub_responses}
+    #
+    #     client = Aws::S3::Client.new(stub_responses: true)
+    #     client.stub_resposnes(:list_buckets, {
+    #       buckets: [{ name: 'my-bucket' }]
+    #     })
+    #
+    #     client.list_buckets.buckets.map(&:name) #=> ['my-bucket']
     #     #=> ['aws-sdk']
     #
+    # Lastly, default stubs can be configured via `Aws.config`:
+    #
+    #     Aws.config[:s3] = {
+    #       stub_responses: {
+    #         list_buckets: { bukets: [{name: 'my-bucket' }] }
+    #       }
+    #     }
+    #
+    #     Aws::S3::Client.new.list_buckets.buckets.map(&:name)
+    #     #=> ['my-bucket']
+    #
     # ## Stubbing Errors
     #
     # When stubbing is enabled, the SDK will default to generate
@@ -73,7 +105,6 @@ def initialize(*args)
     # Calling an operation multiple times will return similar responses.
     # You can configure multiple stubs and they will be returned in sequence.
     #
-    #
     #     client.stub_responses(:head_object, [
     #       'NotFound',
     #       { content_length: 150 },

aws-sdk-core/spec/aws/client_spec.rb

@@ -80,6 +80,16 @@ module Aws
         expect(client.head_bucket(bucket:'aws-sdk').data.to_h).to eq({})
       end
 
+      it 'accepts stubs given to the constructor' do
+        client = S3::Client.new(stub_responses: {
+          list_buckets: { buckets: [{ name: 'b1' }, { name:'b2' }] },
+          get_object: [{ body: 'a' }, { body: 'b' }],
+        })
+        expect(client.list_buckets.buckets.map(&:name)).to eq(%w(b1 b2))
+        expect(client.get_object(bucket:'name', key:'key').body.read).to eq('a')
+        expect(client.get_object(bucket:'name', key:'key').body.read).to eq('b')
+      end
+
     end
   end
 end