Update for testing functions.

docs/testing.md

@@ -0,0 +1,79 @@
+# Testing Functions
+
+`fn` has testing built in that allows you to create inputs and expected outputs and verify the expected output with actual output. 
+
+## Write a Test File
+
+Create a file called `test.json` in your functions directory (beside your `func.yaml` file). Here's a simple example:
+
+```json
+{
+    "tests": [
+        {
+            "input": {
+                "body": {
+                    "name": "Johnny"
+                }
+            },
+            "output": {
+                "body": {
+                    "message": "Hello Johnny"
+                }
+            }
+        },
+        {
+            "input": {
+                "body": ""
+            },
+            "output": {
+                "body": {
+                    "message": "Hello World"
+                }
+            }
+        }
+    ]
+}
+```
+
+The example above has two tests, one with the following input:
+
+```json
+{
+    "name": "Johnny"
+}
+```
+
+and a second one with no input. 
+
+The first one is expected to return a json response with the following:
+
+```json
+{
+    "message": "Hello Johnny"
+}
+```
+
+And the second should return:
+
+```json
+{
+    "message": "Hello World"
+}
+```
+
+## Run Tests
+
+This is simply running:
+
+```sh
+fn test
+```
+
+in your function directory. 
+
+You can also test against a remote `fn` server by using the `--remote` flag. eg:
+
+```sh
+fn test --remote myapp
+```
+