*: refactor methods to support mocking

Additionally, write some tests to ensure the driver method
`startBlacksmithBuilder` handles all exceptions correctly in
both nofallback=true and nofallback=false configurations.

src/__tests__/blacksmith-builder.test.ts

@@ -0,0 +1,80 @@
+import * as core from '@actions/core';
+import * as main from '../main';
+import * as reporter from '../reporter';
+import {getDockerfilePath} from '../context';
+import { getBuilderAddr } from '../setup_builder';
+
+jest.mock('@actions/core', () => ({
+  debug: jest.fn(),
+  warning: jest.fn(),
+  info: jest.fn(),
+  saveState: jest.fn(),
+  getState: jest.fn(),
+  setOutput: jest.fn(),
+  setFailed: jest.fn(),
+  error: jest.fn()
+}));
+
+jest.mock('../context', () => ({
+  getDockerfilePath: jest.fn(),
+  Inputs: jest.fn()
+}));
+
+jest.mock('../reporter', () => ({
+  reportBuilderCreationFailed: jest.fn().mockResolvedValue(undefined)
+}));
+
+jest.mock('../setup_builder', () => ({
+  getBuilderAddr: jest.fn()
+}));
+
+describe('startBlacksmithBuilder', () => {
+  let mockInputs;
+
+  beforeEach(() => {
+    jest.clearAllMocks();
+    mockInputs = {nofallback: false};
+  });
+
+  test('should handle missing dockerfile path with nofallback=false', async () => {
+    (getDockerfilePath as jest.Mock).mockReturnValue(null);
+
+    const result = await main.startBlacksmithBuilder(mockInputs);
+
+    expect(result).toEqual({addr: null, buildId: null, exposeId: ''});
+    expect(core.warning).toHaveBeenCalledWith('Error during Blacksmith builder setup: Failed to resolve dockerfile path. Falling back to a local build.');
+    expect(reporter.reportBuilderCreationFailed).toHaveBeenCalledWith(new Error('Failed to resolve dockerfile path'));
+  });
+
+  test('should handle missing dockerfile path with nofallback=true', async () => {
+    (getDockerfilePath as jest.Mock).mockReturnValue(null);
+    mockInputs.nofallback = true;
+
+    await expect(main.startBlacksmithBuilder(mockInputs)).rejects.toThrow('Failed to resolve dockerfile path');
+    expect(core.warning).not.toHaveBeenCalled();
+    expect(reporter.reportBuilderCreationFailed).toHaveBeenCalledWith(new Error('Failed to resolve dockerfile path'));
+  });
+
+  test('should handle error in getBuilderAddr with nofallback=false', async () => {
+    (getDockerfilePath as jest.Mock).mockReturnValue('/path/to/Dockerfile');
+    (getBuilderAddr as jest.Mock).mockRejectedValue(new Error('Failed to obtain Blacksmith builder'));
+
+    mockInputs.nofallback = false;
+    const result = await main.startBlacksmithBuilder(mockInputs);
+
+    expect(result).toEqual({addr: null, buildId: null, exposeId: ''});
+    expect(core.warning).toHaveBeenCalledWith('Error during Blacksmith builder setup: Failed to obtain Blacksmith builder. Falling back to a local build.');
+    expect(reporter.reportBuilderCreationFailed).toHaveBeenCalledWith(new Error('Failed to obtain Blacksmith builder'));
+  });
+
+  test('should handle error in getBuilderAddr with nofallback=true', async () => {
+    (getDockerfilePath as jest.Mock).mockReturnValue('/path/to/Dockerfile');
+    const error = new Error('Failed to obtain Blacksmith builder');
+    (getBuilderAddr as jest.Mock).mockRejectedValue(error);
+    mockInputs.nofallback = true;
+
+    await expect(main.startBlacksmithBuilder(mockInputs)).rejects.toThrow(error);
+    expect(core.warning).not.toHaveBeenCalled();
+    expect(reporter.reportBuilderCreationFailed).toHaveBeenCalledWith(error);
+  });
+});