fn: support for functions testing (#379)

* fn: add test framework

* fn: make routes creation smarter

* fn: add testframework examples

* fn: remove unnecessary dependency

* fn: update doc

* fn: fix consistenty between runff, runlocaltest and runremotetest

docs/function-file.md

@@ -27,7 +27,8 @@ build:
 route updated to use it.
 
 `path` (optional) allows you to overwrite the calculated route from the path
-position. You may use it to override the calculated route.
+position. You may use it to override the calculated route. If you plan to use
+`fn test --remote=""`, this is mandatory.
 
 `version` represents current version of the function. When deploying, it is
 appended to the image as a tag.
@@ -47,4 +48,32 @@ during functions execution.
 
 `build` (optional) is an array of shell calls which are used to helping building
 the image. These calls are executed before `fn` calls `docker build` and
-`docker push`.
+`docker push`.
+
+## Testing functions
+
+`tests` (optional) is an array of tests that can be used to valid functions both
+locally and remotely. It has the following structure
+
+```yaml
+tests:
+- name: envvar
+  in: "inserted stdin"
+  out: "expected stdout"
+  err: "expected stderr"
+  env:
+    envvar: trololo
+```
+
+`in` (optional) is a string that is going to be sent to the file's declared
+function.
+
+`out` (optional) is the expected output for this function test. It is present
+both in local and remote executions.
+
+`err` (optional) similar to `out`, however it read from `stderr`. It is only
+available for local machine tests.
+
+`env` (optional) is a map of environment variables that are injected during
+tests.
+