Create BESTPRACTICES.md (#39)

Author: jreock

BESTPRACTICES.md

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+# Best Practices Guide
+
+This document outlines best practices for developing plugins in React and TypeScript for the [Cortex.io](http://cortex.io/) Plugin Community. Following these guidelines ensures consistent, maintainable, and high-quality plugins.
+
+## Project Structure
+
+Plugins should be Scaffolded in Cortex using the “Cortex Plugin” template and will match the following project structure:
+
+```jsx
+__mocks__/
+src/
+   api/
+      Cortex.ts
+   assets/
+      logo.svg
+   components/
+      App.test.tsx
+      App.tsx
+      ErrorBoundary.tsx
+      PluginContext.tsx
+   baseStyles.css
+   index.html
+   index.tsx
+   typings.d.ts   
+.eslintignore
+.eslintrc.js
+.gitignore
+.prettierignore
+README.md
+babel.config.js
+cortex.yaml
+jest.config.js
+package.json
+setupTests.ts
+tsconfig.json
+webpack.config.js
+```
+
+## Code Style
+
+1. **Linting and Formatting**:
+    - Use **ESLint** with React and TypeScript plugins to enforce consistent code style.
+    - Use **Prettier** for formatting. Configure Prettier to auto-format code on save.
+
+### Configuration for ESLint
+
+```
+// .eslintrc.js
+module.exports = {
+  env: {
+    browser: true,
+    es2021: true,
+  },
+  extends: [
+    "plugin:react/jsx-runtime",
+    "plugin:react-hooks/recommended",
+    "standard-with-typescript",
+    "prettier",
+  ],
+  overrides: [],
+  parserOptions: {
+    ecmaVersion: "latest",
+    project: "tsconfig.json",
+    sourceType: "module",
+    tsconfigRootDir: __dirname,
+  },
+  plugins: ["react"],
+  rules: {
+    // conflicts with no-extra-boolean-cast
+    "@typescript-eslint/strict-boolean-expressions": "off",
+    "no-console": ["error", { allow: ["warn", "error"] }],
+  },
+  settings: {
+    react: {
+      version: "detect",
+    },
+  },
+};
+```
+
+## Unit Testing
+
+- **Coverage Requirement**: Aim for 80% test coverage. Prioritize testing key functions and complex logic. You can use Istanbul (baked into Yarn) to check your coverage, like:
+
+```markup
+yarn test --coverage
+```
+
+- **Testing Library**: Use **Jest** and **React Testing Library** for unit tests.
+- **Testing Standards**:
+    - Test each component’s rendered output.
+    - Mock API calls and test component behavior based on different responses.
+    - Test edge cases and error handling.
+
+## Example Unit Test
+
+```jsx
+  it("Shows a page if page is found", async () => {
+    fetchMock.mockResponses(
+      [JSON.stringify(serviceYaml), { status: 200 }],
+      [JSON.stringify(mockPageContent), { status: 200 }]
+    );
+
+    render(<PageContent />);
+    await waitFor(() => {
+      expect(screen.queryByText("AppDirect Runbook")).toBeInTheDocument();
+    });
+  });
+```
+
+## Documentation and Comments
+
+1. **README**: Provide a clear README file for each plugin with installation, usage, and basic configuration instructions, ideally with a screenshot of the plugin.
+2. Clearly document which types of entities the plugin is compatible with
+3. **Code Comments**:
+    - Use comments sparingly for complex logic or non-obvious code.
+    - Avoid redundant comments that describe straightforward code.