feat: allow switching branches (#73)

* implemented checkout and added test cases

* updated readme

README.md

@@ -369,7 +369,7 @@ await github.setup();
 
 #### Utility functions
 
-There multiple utility functions available to extract information about the state of the repositories.
+There multiple utility functions available to extract information about the state of the repositories and perform some action on them.
 
 ```typescript
 const github = new MockGithub("path to config");
@@ -422,6 +422,11 @@ const branches = github.repo.getBranchState("repoA");
  * {  path: string, branch: string }[]
  */
 const repoFs = await github.repo.getFileSystemState("repoA");
+
+/**
+ * Checkout the given branch in the given repo. Will throw an error if the repo or the branch does not exist
+ */ 
+await github.repo.checkout("repoA", "branchA");
 ```
 
 ### Env

src/github/repository/state/repository-state.ts

@@ -15,6 +15,7 @@ import {
   RepositoryStateMethods,
   State,
 } from "@mg/github/repository/state/repository-state.types";
+import simpleGit from "simple-git";
 
 export class RepositoryState implements RepositoryStateMethods {
   private repositories: Repositories;
@@ -83,6 +84,28 @@ export class RepositoryState implements RepositoryStateMethods {
     }
   }
 
+  async checkout(repositoryName: string, branch: string): Promise<void> {
+    const repoPath = this.getPath(repositoryName);
+    const currBranches = this.getBranchState(repositoryName);
+    if (!repoPath) {
+      throw new Error("Repository does not exist");
+    }
+
+    if (
+      !currBranches?.localBranches.includes(branch) &&
+      !currBranches?.pushedBranches.includes(branch)
+    ) {
+      throw new Error("Branch does not exist");
+    }
+
+    await simpleGit(repoPath).checkout(branch);
+
+    this.repositories[repositoryName] = {
+      ...this.repositories[repositoryName],
+      currentBranch: branch
+    };
+  }
+
   async getFileSystemState(
     repositoryName: string
   ): Promise<FileState[] | undefined> {

src/github/repository/state/repository-state.types.ts

@@ -26,4 +26,5 @@ export interface RepositoryStateMethods {
   getOwner(repositoryName: string): string | undefined;
   getBranchState(repositoryName: string): BranchState | undefined;
   getFileSystemState(repositoryName: string): Promise<FileState[] | undefined>;
+  checkout(repositoryName: string, branch: string): Promise<void>;
 }

test/github/repository/state/repository-state.test.ts

@@ -8,9 +8,12 @@ import {
 } from "@mg/github/repository/history/repository-history.types";
 import { DEFAULT_BRANCH } from "@mg/github/repository/repository.constants";
 import { RepositoryState } from "@mg/github/repository/state/repository-state";
+import simpleGit from "simple-git";
 
 const setupPath = __dirname;
 
+jest.mock("simple-git");
+
 describe("getFileSystemState", () => {
   test("undefined repository", async () => {
     const repoState = new RepositoryState({}, setupPath);
@@ -320,3 +323,48 @@ describe("getState", () => {
     });
   });
 });
+
+describe("checkout", () => {
+  test.each([
+    ["repository does not exist", {}],
+    [
+      "repository exists but branch doesn't",
+      {
+        repoA: {
+          owner: "owner",
+          localBranches: ["local1", "local2"],
+          pushedBranches: ["pushed1", "pushed2"],
+          currentBranch: "local1",
+          forkedFrom: "project-forked",
+        },
+      },
+    ],
+  ])("%p", async (_title, config) => {
+    const repoState = new RepositoryState(config, setupPath);
+    await expect(repoState.checkout("repoA", "branchA")).rejects.toThrowError();
+  });
+
+  test("repository and branch does exist", async () => {
+    const simpleGitMock = simpleGit as jest.Mock;
+    const checkoutMock = jest.fn(async _branch => undefined);
+
+    simpleGitMock.mockReturnValue({
+      checkout: checkoutMock
+    });
+
+    const repoState = new RepositoryState({
+      repoA: {
+        owner: "owner",
+        localBranches: ["local1", "local2"],
+        pushedBranches: ["pushed1", "pushed2"],
+        currentBranch: "local1",
+        forkedFrom: "project-forked",
+      },
+    }, setupPath);
+
+    await expect(repoState.checkout("repoA", "pushed1")).resolves.not.toThrowError();
+    expect(repoState.getBranchState("repoA")).toMatchObject({currentBranch: "pushed1"});
+    expect(simpleGitMock).toHaveBeenCalledWith(repoState.getPath("repoA"));
+    expect(checkoutMock).toHaveBeenCalledWith("pushed1");
+  });
+});