fix: allow dry run to check if function exists

README.md

@@ -103,6 +103,7 @@ Validate parameters and permissions without any function code or configuration m
           code-artifacts-dir: my-code-artifacts-dir
           dry-run: true
 ```
+ **Note**: Dry run will still call `GetFunctionConfiguration` to check if the function exists and perform configuration diffs against what's currently deployed.
 ## Build from Source
 
 To automate building your source code, add a build step based on your runtime and build process. This build step should be performed before the AWS Lambda Deploy step, and AWS Lambda Deploy's `code-artifacts-dir` parameter will typically be set to the build step's code artifact output directory.

__tests__/dry_run_mode.test.js

@@ -38,4 +38,73 @@ describe('Dry Run Mode Tests', () => {
 
     await mainModule.run();
   });
-});
+
+  test('should check if function exists even in dry run mode', async () => {
+    const mockSend = jest.fn()
+      // First call: checkFunctionExists - function exists
+      .mockResolvedValueOnce({ Runtime: 'nodejs18.x' })
+      // Second call: GetFunctionConfigurationCommand for config check
+      .mockResolvedValueOnce({ Runtime: 'nodejs18.x', MemorySize: 256 })
+      // Third call: UpdateFunctionCodeCommand dry run
+      .mockResolvedValueOnce({
+        FunctionArn: 'arn:aws:lambda:us-east-1:123456789012:function:test-function',
+        Version: '$LATEST'
+      });
+
+    const mockClient = { send: mockSend };
+    LambdaClient.mockImplementation(() => mockClient);
+
+    validations.validateAllInputs = jest.fn().mockReturnValue({
+      valid: true,
+      functionName: 'test-function',
+      parsedEnvironment: {},
+      dryRun: true,
+      codeArtifactsDir: './code'
+    });
+
+    jest.spyOn(mainModule, 'packageCodeArtifacts').mockResolvedValue('/tmp/test.zip');
+    const fs = require('fs/promises');
+    fs.readFile = jest.fn().mockResolvedValue(Buffer.from('test'));
+
+    await mainModule.run();
+
+    // Verify that checkFunctionExists was called (first send call should be GetFunctionConfigurationCommand)
+    expect(mockSend).toHaveBeenCalled();
+    expect(mockSend.mock.calls[0][0].constructor.name).toEqual('GetFunctionConfigurationCommand');
+
+    // Verify dry run proceeded successfully
+    expect(core.info).toHaveBeenCalledWith('Checking if test-function exists');
+    expect(core.info).toHaveBeenCalledWith('DRY RUN MODE: No AWS resources will be created or modified');
+    expect(core.setFailed).not.toHaveBeenCalledWith('DRY RUN MODE can only be used for updating function code of existing functions');
+  });
+
+  test('should fail dry run mode when function does not exist', async () => {
+    const mockSend = jest.fn()
+      // checkFunctionExists - function does not exist (ResourceNotFoundException)
+      .mockRejectedValueOnce({ name: 'ResourceNotFoundException' });
+
+    const mockClient = { send: mockSend };
+    LambdaClient.mockImplementation(() => mockClient);
+
+    validations.validateAllInputs = jest.fn().mockReturnValue({
+      valid: true,
+      functionName: 'non-existent-function',
+      parsedEnvironment: {},
+      dryRun: true,
+      codeArtifactsDir: './code'
+    });
+
+    jest.spyOn(mainModule, 'packageCodeArtifacts').mockResolvedValue('/tmp/test.zip');
+
+    await mainModule.run();
+
+    // Verify that checkFunctionExists was called (first send call should be GetFunctionConfigurationCommand)
+    expect(mockSend).toHaveBeenCalled();
+    expect(mockSend.mock.calls[0][0].constructor.name).toEqual('GetFunctionConfigurationCommand');
+
+    // Verify dry run failed with correct error message
+    expect(core.info).toHaveBeenCalledWith('Checking if non-existent-function exists');
+    expect(core.info).toHaveBeenCalledWith('DRY RUN MODE: No AWS resources will be created or modified');
+    expect(core.setFailed).toHaveBeenCalledWith('DRY RUN MODE can only be used for updating function code of existing functions');
+  });
+});

__tests__/s3_key_generation.test.js

@@ -37,17 +37,26 @@ describe('S3 Key Generation and Dry Run Tests', () => {
   });
 
   test('should log dry run message and fail when function does not exist', async () => {
+    const mockSend = jest.fn()
+      // checkFunctionExists - function does not exist (ResourceNotFoundException)
+      .mockRejectedValueOnce({ name: 'ResourceNotFoundException' });
+
+    const mockClient = { send: mockSend };
+    LambdaClient.mockImplementation(() => mockClient);
+
     validations.validateAllInputs = jest.fn().mockReturnValue({
       valid: true,
       functionName: 'test-function',
-      dryRun: true
+      parsedEnvironment: {},
+      dryRun: true,
+      codeArtifactsDir: './code'
     });
 
-    jest.spyOn(mainModule, 'checkFunctionExists').mockResolvedValue(false);
+    jest.spyOn(mainModule, 'packageCodeArtifacts').mockResolvedValue('/tmp/test.zip');
 
     await mainModule.run();
 
     expect(core.info).toHaveBeenCalledWith('DRY RUN MODE: No AWS resources will be created or modified');
     expect(core.setFailed).toHaveBeenCalledWith('DRY RUN MODE can only be used for updating function code of existing functions');
   });
-});
+});