🧹 Add tests that run the whole action (#149)

__mocks__/@actions/github.ts

@@ -0,0 +1,32 @@
+export const context = {
+  payload: {
+    pull_request: {
+      number: 123,
+    },
+  },
+  repo: {
+    owner: "monalisa",
+    repo: "helloworld",
+  },
+};
+
+const mockApi = {
+  issues: {
+    addLabels: jest.fn(),
+    removeLabel: jest.fn(),
+  },
+  paginate: jest.fn(),
+  pulls: {
+    get: jest.fn().mockResolvedValue({}),
+    listFiles: {
+      endpoint: {
+        merge: jest.fn().mockReturnValue({}),
+      },
+    },
+  },
+  repos: {
+    getContents: jest.fn(),
+  },
+};
+
+export const GitHub = jest.fn().mockImplementation(() => mockApi);