Context test tools (#168)

* add enzyme test helper with lingui provider

* add router context to enzyme test helper

* get 18n, router, & config contexts rendering together in enzyme helper

* add config context to enzyme helpers

* add network and dialog contexts to enzymeHelpers

* convert OrganizationForm tests to use new mountWithContexts helper

* default all context value keys to default unless provided

* document use of mountWithContexts()

* fix typo in CONTRIBUTING.md

* update Organizations to use mountWithContext

CONTRIBUTING.md

@@ -183,4 +183,33 @@ this.state = {
   somethingD: {},
   somethingE: '',
 }
-```
+```
+
+### Testing components that use contexts
+
+We have several React contexts that wrap much of the app, including those from react-router, lingui, and some of our own. When testing a component that depends on one or more of these, you can use the `mountWithContexts()` helper function found in `__tests__/enzymeHelpers.jsx`. This can be used just like Enzyme's `mount()` function, except it will wrap the component tree with the necessary context providers and basic stub data.
+
+If you want to stub the value of a context, or assert actions taken on it, you can customize a contexts value by passing a second parameter to `mountWithContexts`. For example, this provides a custom value for the `Network` context:
+
+```
+const network = {
+  api: {
+    getOrganizationInstanceGroups: jest.fn(),
+  }
+};
+mountWithContexts(<OrganizationForm />, {
+  context: { network },
+});
+```
+
+In this test, when the `OrganizationForm` calls `api.getOrganizationInstanceGroups` from the network context, it will invoke the provided stub. You can assert that this stub is invoked when you expect or to provide stubbed data.
+
+The object containing context values looks for five known contexts, identified by the keys `linguiPublisher`, `router`, `config`, `network`, and `dialog` — the latter three each referring to the contexts defined in `src/contexts`. You can pass `false` for any of these values, and the corresponding context will be omitted from your test. For example, this will mount your component without the dialog context:
+
+```
+mountWithContexts(<Organization />< {
+  context: {
+    dialog: false,
+  }
+});
+```