support a seed option

Author: Raynos

README.md

@@ -59,7 +59,8 @@ playdoh-server/config := (dirname: String, opts?: {
     argv?: Array<String>,
     dc?: String,
     blackList?: Array<String>,
-    env?: Object<String, String>
+    env?: Object<String, String>,
+    seed?: Object<String, Any>
 }) => {
     get: (keypath?: String) => Any,
     set: (keypath: String, value: Any) => void,
@@ -101,6 +102,7 @@ Below are the sources it reads in order of least precendence.
  - a object literal based on command line arguments. i.e. if 
     you pass `--foo='bar' --bar.baz='bob'` you will get
     `{ "foo": "bar", "bar": { "baz": "bob" } }`
+ - a seed object of manual overwrites for testing purposes.
 
 The config loader also uses `config-chain` for the actual
   loading logic so you can read [their docs][config-chain]
@@ -182,6 +184,21 @@ If you prefer to not have this variable configured through
   the environment or want to call it something else then you
   can pass in `{ NODE_ENV: whatever }` as `opts.env`
 
+#### `opts.seed`
+
+`opts.seed` is optional, it can be set to an object
+
+If it exists we will merge the seed object into the config
+  data we have fetched. seed overwrites all the other sources
+  of configuration.
+
+The `seed` option is very useful for testing purposes, it allows
+  you to overwrite the configuration that your application would
+  load with test specific properties.
+
+This is an alternative to the `NODE_ENV=test `pattern, we highly
+  recommend that you do not have a `test.json` file at all.
+
 #### `var value = config.get(keypath)`
 
 `config.get(keypath)` will return the value at a keypath. The 

index.js

@@ -149,6 +149,8 @@ function fetchConfigSync(dirname, opts) {
         "transports" for loading configuration from disk
     */
     var configTree = configChain(
+        // the seed option overwrites everything
+        opts.seed || null,
         // include all CLI arguments
         makeDeep(cliArgs),
         // load file from --config someFilePath

test/index.js

@@ -296,3 +296,28 @@ test('config.set(undefined) throws', function (assert) {
     assert.end();
 
 });
+
+test('config({ seed: seed })', function (assert) {
+    var argv = [
+        '--foo', 'bar',
+        '--baz.lulz', 'some value',
+        '--baz.foob', 'thingy'
+    ];
+
+    var config = fetchConfig(__dirname, {
+        argv: argv,
+        seed: {
+            baz: {
+                lulz: 42
+            },
+            bar: 'foo'
+        }
+    });
+
+    assert.equal(config.get('foo'), 'bar');
+    assert.equal(config.get('baz.lulz'), 42);
+    assert.equal(config.get('baz.foob'), 'thingy');
+    assert.equal(config.get('bar'), 'foo');
+
+    assert.end();
+});