diff --git a/packages/amplify-appsync-simulator/src/__tests__/index.test.ts b/packages/amplify-appsync-simulator/src/__tests__/index.test.ts
index 3a72a74ae02..5f496ee57e2 100644
--- a/packages/amplify-appsync-simulator/src/__tests__/index.test.ts
+++ b/packages/amplify-appsync-simulator/src/__tests__/index.test.ts
@@ -9,6 +9,7 @@ import {
   AppSyncMockFile,
   AppSyncSimulatorBaseResolverConfig,
   RESOLVER_KIND,
+  AppSyncSimulatorUnitResolverConfig,
 } from '../type-definition';
 
 jest.mock('../schema');
@@ -48,9 +49,10 @@ describe('AmplifyAppSyncSimulator', () => {
   });
 
   it('should retain the original configuration when config has error', () => {
-    const resolver: AppSyncSimulatorBaseResolverConfig = {
+    const resolver: AppSyncSimulatorUnitResolverConfig = {
       fieldName: 'echo',
       typeName: 'Query',
+      dataSourceName: 'echoFn',
       kind: RESOLVER_KIND.UNIT,
       requestMappingTemplateLocation: 'missing/Resolver.req.vtl',
       responseMappingTemplateLocation: 'missing/Resolver.resp.vtl',
diff --git a/packages/amplify-appsync-simulator/src/__tests__/resolvers/pipeline-resolver.test.ts b/packages/amplify-appsync-simulator/src/__tests__/resolvers/pipeline-resolver.test.ts
new file mode 100644
index 00000000000..798da1505d7
--- /dev/null
+++ b/packages/amplify-appsync-simulator/src/__tests__/resolvers/pipeline-resolver.test.ts
@@ -0,0 +1,202 @@
+import { AppSyncPipelineResolver } from '../../resolvers/pipeline-resolver';
+import { AmplifyAppSyncSimulator } from '../..';
+import { RESOLVER_KIND, AppSyncSimulatorPipelineResolverConfig } from '../../type-definition';
+describe('Pipeline Resolvers', () => {
+  const getFunction = jest.fn();
+  const getMappingTemplate = jest.fn();
+  const simulatorContext: AmplifyAppSyncSimulator = ({
+    getFunction,
+    getMappingTemplate,
+  } as any) as AmplifyAppSyncSimulator;
+  let baseConfig;
+  beforeEach(() => {
+    jest.resetAllMocks();
+    getFunction.mockReturnValue({ resolve: () => 'foo' });
+    getMappingTemplate.mockReturnValue('TEMPLATE');
+    baseConfig = {
+      fieldName: 'fn1',
+      typeName: 'Query',
+      kind: RESOLVER_KIND.PIPELINE,
+      functions: ['fn1', 'fn2'],
+    };
+  });
+  it('should initialize when the request and response mapping templates are inline templates', () => {
+    const config: AppSyncSimulatorPipelineResolverConfig = {
+      ...baseConfig,
+      requestMappingTemplate: 'request',
+      responseMappingTemplate: 'response',
+    };
+    expect(() => new AppSyncPipelineResolver(config, simulatorContext)).not.toThrow();
+    expect(getMappingTemplate).not.toHaveBeenCalled();
+  });
+
+  it('should work when the request and response mapping are external template', () => {
+    const config: AppSyncSimulatorPipelineResolverConfig = {
+      ...baseConfig,
+      requestMappingTemplateLocation: 'resolvers/request',
+      responseMappingTemplateLocation: 'resolvers/response',
+    };
+    expect(() => new AppSyncPipelineResolver(config, simulatorContext)).not.toThrow();
+    expect(getMappingTemplate).toHaveBeenCalledTimes(2);
+  });
+
+  it('should throw error when request templates are missing', () => {
+    getMappingTemplate.mockImplementation(() => {
+      throw new Error('Missing template');
+    });
+    expect(() => new AppSyncPipelineResolver(baseConfig, simulatorContext)).toThrowError('Missing request mapping template');
+    expect(getMappingTemplate).toHaveBeenCalled();
+  });
+
+  describe('resolve', () => {
+    let resolver: AppSyncPipelineResolver;
+    const baseConfig: AppSyncSimulatorPipelineResolverConfig = {
+      fieldName: 'fn1',
+      typeName: 'Query',
+      kind: RESOLVER_KIND.PIPELINE,
+      functions: ['fn1', 'fn2'],
+      requestMappingTemplateLocation: 'request',
+      responseMappingTemplateLocation: 'response',
+    };
+    let templates;
+    let fnImpl;
+    beforeEach(() => {
+      fnImpl = {
+        fn1: {
+          resolve: jest.fn().mockImplementation((source, args, stash, prevResult, context, info) => {
+            return {
+              result: 'FN1-RESULT',
+              stash: { ...stash, exeSeq: [...(stash.exeSeq || []), 'fn1'] },
+            };
+          }),
+        },
+        fn2: {
+          resolve: jest.fn().mockImplementation((source, args, stash, prevResult, context, info) => {
+            return {
+              result: 'FN2-RESULT',
+              stash: { ...stash, exeSeq: [...(stash.exeSeq || []), 'fn2'] },
+            };
+          }),
+        },
+      };
+      getFunction.mockImplementation(fnName => fnImpl[fnName]);
+      templates = {
+        request: {
+          render: jest.fn().mockImplementation(({ stash }) => ({
+            result: 'REQUEST_TEMPLATE_RESULT',
+            errors: [],
+            stash: { ...stash, exeSeq: [...(stash.exeSeq || []), 'REQUEST-MAPPING-TEMPLATE'] },
+          })),
+        },
+        response: {
+          render: jest.fn().mockImplementation(({ stash }) => ({
+            result: 'RESPONSE_TEMPLATE_RESULT',
+            errors: [],
+            stash: { ...stash, exeSeq: [...stash.exeSeq, 'fn2'] },
+          })),
+        },
+      };
+
+      getMappingTemplate.mockImplementation(templateName => templates[templateName]);
+      resolver = new AppSyncPipelineResolver(baseConfig, simulatorContext);
+    });
+
+    it('should render requestMapping template', async () => {
+      const source = 'SOURCE';
+      const args = { arg1: 'val' };
+      const context = {
+        appsyncErrors: [],
+      };
+      const info = {};
+      const result = await resolver.resolve(source, args, context, info);
+      expect(result).toEqual('RESPONSE_TEMPLATE_RESULT');
+      expect(templates['request'].render).toHaveBeenCalledWith(
+        {
+          source,
+          arguments: args,
+          stash: {},
+        },
+        context,
+        info,
+      );
+
+      expect(getMappingTemplate).toHaveBeenCalledTimes(4); // 2 times in constructor and 2 times for resolving
+      expect(getFunction).toHaveBeenCalled();
+    });
+
+    it('should pass stash and prevResult between functions and templates', async () => {
+      const source = 'SOURCE';
+      const args = { arg1: 'val' };
+      const context = {
+        appsyncErrors: [],
+      };
+      const info = {};
+      const result = await resolver.resolve(source, args, context, info);
+      expect(result).toEqual('RESPONSE_TEMPLATE_RESULT');
+      expect(fnImpl.fn1.resolve).toHaveBeenLastCalledWith(
+        source,
+        args,
+        { exeSeq: ['REQUEST-MAPPING-TEMPLATE'] },
+        'REQUEST_TEMPLATE_RESULT',
+        context,
+        info,
+      );
+
+      expect(fnImpl.fn2.resolve).toHaveBeenLastCalledWith(
+        source,
+        args,
+        { exeSeq: ['REQUEST-MAPPING-TEMPLATE', 'fn1'] },
+        'FN1-RESULT',
+        context,
+        info,
+      );
+
+      expect(templates['response'].render).toHaveBeenCalledWith(
+        {
+          source,
+          arguments: args,
+          prevResult: 'FN2-RESULT',
+          stash: { exeSeq: ['REQUEST-MAPPING-TEMPLATE', 'fn1', 'fn2'] },
+        },
+        context,
+        info,
+      );
+    });
+
+    it('should not call response mapping template when #return is called', async () => {
+      templates.request.render.mockReturnValue({ isReturn: true, result: 'REQUEST_TEMPLATE_RESULT', templateErrors: [] });
+      const source = 'SOURCE';
+      const args = { arg1: 'val' };
+      const context = {
+        appsyncErrors: [],
+      };
+      const info = {};
+      const result = await resolver.resolve(source, args, context, info);
+      expect(result).toEqual('REQUEST_TEMPLATE_RESULT');
+    });
+
+    it('should merge template errors', async () => {
+      templates.request.render.mockReturnValue({
+        isReturn: false,
+        stash: {},
+        result: 'REQUEST_TEMPLATE_RESULT',
+        errors: ['REQUEST_TEMPLATE_ERROR'],
+      });
+      templates.response.render.mockReturnValue({
+        isReturn: false,
+        result: 'RESPONSE_TEMPLATE_RESULT',
+        errors: ['RESPONSE_TEMPLATE_ERROR'],
+      });
+
+      const source = 'SOURCE';
+      const args = { arg1: 'val' };
+      const context = {
+        appsyncErrors: [],
+      };
+      const info = {};
+      const result = await resolver.resolve(source, args, context, info);
+      expect(result).toEqual('RESPONSE_TEMPLATE_RESULT');
+      expect(context.appsyncErrors).toEqual(['REQUEST_TEMPLATE_ERROR', 'RESPONSE_TEMPLATE_ERROR']);
+    });
+  });
+});
diff --git a/packages/amplify-appsync-simulator/src/__tests__/resolvers/unit-resolver.test.ts b/packages/amplify-appsync-simulator/src/__tests__/resolvers/unit-resolver.test.ts
new file mode 100644
index 00000000000..b457ca10253
--- /dev/null
+++ b/packages/amplify-appsync-simulator/src/__tests__/resolvers/unit-resolver.test.ts
@@ -0,0 +1,176 @@
+import { AppSyncUnitResolver } from '../../resolvers/unit-resolver';
+import { AmplifyAppSyncSimulator } from '../..';
+import { RESOLVER_KIND, AppSyncSimulatorUnitResolverConfig } from '../../type-definition';
+
+describe('Unit resolver', () => {
+  const getDataLoader = jest.fn();
+  const getMappingTemplate = jest.fn();
+  const simulatorContext: AmplifyAppSyncSimulator = ({
+    getDataLoader,
+    getMappingTemplate,
+  } as any) as AmplifyAppSyncSimulator;
+  let baseConfig;
+
+  beforeEach(() => {
+    jest.resetAllMocks();
+    getDataLoader.mockReturnValue({
+      load: () => {
+        return 'DATA';
+      },
+    });
+    getMappingTemplate.mockReturnValue('TEMPLATE');
+    baseConfig = {
+      fieldName: 'getPost',
+      typeName: 'Query',
+      kind: RESOLVER_KIND.UNIT,
+      dataSourceName: 'TodoTable',
+    };
+  });
+
+  it('should initialize when the request and response mapping templates are inline templates', () => {
+    const config: AppSyncSimulatorUnitResolverConfig = {
+      ...baseConfig,
+      requestMappingTemplate: 'request',
+      responseMappingTemplate: 'response',
+    };
+    expect(() => new AppSyncUnitResolver(config, simulatorContext)).not.toThrow();
+    expect(getMappingTemplate).not.toHaveBeenCalled();
+  });
+
+  it('should work when the request and response mapping are external template', () => {
+    const config: AppSyncSimulatorUnitResolverConfig = {
+      ...baseConfig,
+      requestMappingTemplateLocation: 'resolvers/request',
+      responseMappingTemplateLocation: 'resolvers/response',
+    };
+    expect(() => new AppSyncUnitResolver(config, simulatorContext)).not.toThrow();
+    expect(getMappingTemplate).toHaveBeenCalledTimes(2);
+  });
+
+  it('should throw error when request templates are missing', () => {
+    getMappingTemplate.mockImplementation(() => {
+      throw new Error('Missing template');
+    });
+    expect(() => new AppSyncUnitResolver(baseConfig, simulatorContext)).toThrowError('Missing request mapping template');
+    expect(getMappingTemplate).toHaveBeenCalled();
+  });
+
+  describe('resolve', () => {
+    let templates;
+    let resolver;
+
+    const info = {};
+    const DATA_FROM_DATA_SOURCE = 'DATA FROM DATA SOURCE';
+    const REQUEST_TEMPLATE_RESULT = {
+      version: '2017-02-29',
+      result: 'REQUEST_TEMPLATE_RESULT',
+    };
+    const RESPONSE_TEMPLATE_RESULT = {
+      version: '2017-02-29',
+      data: 'RESPONSE_TEMPLATE_RESULT',
+    };
+    let dataFetcher;
+
+    const source = 'SOURCE';
+    const args = { key: 'value' };
+    const context = {
+      appsyncErrors: [],
+    };
+
+    beforeEach(() => {
+      context.appsyncErrors = [];
+      templates = {
+        request: {
+          render: jest.fn().mockImplementation(() => ({
+            result: REQUEST_TEMPLATE_RESULT,
+            errors: [],
+          })),
+        },
+        response: {
+          render: jest.fn().mockImplementation(() => ({
+            result: RESPONSE_TEMPLATE_RESULT,
+            errors: [],
+          })),
+        },
+      };
+
+      dataFetcher = jest.fn().mockResolvedValue(DATA_FROM_DATA_SOURCE);
+
+      getDataLoader.mockReturnValue({
+        load: dataFetcher,
+      });
+      getMappingTemplate.mockImplementation(templateName => {
+        return templates[templateName];
+      });
+
+      resolver = new AppSyncUnitResolver(
+        { ...baseConfig, requestMappingTemplateLocation: 'request', responseMappingTemplateLocation: 'response' },
+        simulatorContext,
+      );
+    });
+
+    it('should resolve', async () => {
+      const result = await resolver.resolve(source, args, context, info);
+      expect(result).toEqual(RESPONSE_TEMPLATE_RESULT);
+      expect(templates.request.render).toHaveBeenCalledWith({ source, arguments: args }, context, info);
+      expect(dataFetcher).toHaveBeenCalledWith(REQUEST_TEMPLATE_RESULT);
+      expect(getDataLoader).toBeCalledWith('TodoTable');
+      expect(templates.response.render).toHaveBeenCalledWith({ source, arguments: args, result: DATA_FROM_DATA_SOURCE }, context, info);
+    });
+
+    it('should not call the response mapping template with template version 2017-02-29 and data fetcher throws error', async () => {
+      dataFetcher.mockImplementation(() => {
+        throw new Error('Some request template error');
+      });
+
+      await expect(() => resolver.resolve(source, args, context, info)).rejects.toThrowError('Some request template error');
+      expect(templates.request.render).toHaveBeenCalledWith({ source, arguments: args }, context, info);
+      expect(dataFetcher).toHaveBeenCalledWith(REQUEST_TEMPLATE_RESULT);
+      expect(getDataLoader).toBeCalledWith('TodoTable');
+      expect(templates.response.render).not.toHaveBeenCalled();
+    });
+
+    it('should render response mapping when data fetcher throws error and template version is 2018-05-29', async () => {
+      REQUEST_TEMPLATE_RESULT.version = '2018-05-29';
+      const error = new Error('Some request template error');
+      dataFetcher.mockImplementation(() => {
+        throw error;
+      });
+      const result = await resolver.resolve(source, args, context, info);
+      expect(result).toEqual(RESPONSE_TEMPLATE_RESULT);
+      expect(templates.request.render).toHaveBeenCalledWith({ source, arguments: args }, context, info);
+      expect(dataFetcher).toHaveBeenCalledWith(REQUEST_TEMPLATE_RESULT);
+      expect(getDataLoader).toBeCalledWith('TodoTable');
+      expect(templates.response.render).toHaveBeenCalledWith({ source, arguments: args, error: error, result: null }, context, info);
+    });
+
+    it('should not render response mapping template when #return is used in request mapping template', async () => {
+      REQUEST_TEMPLATE_RESULT.version = '2018-05-29';
+      templates.request.render.mockReturnValue({
+        ...REQUEST_TEMPLATE_RESULT,
+        errors: [],
+        isReturn: true,
+      });
+
+      const result = await resolver.resolve(source, args, context, info);
+      expect(result).toEqual(REQUEST_TEMPLATE_RESULT.result);
+      expect(templates.request.render).toHaveBeenCalledWith({ source, arguments: args }, context, info);
+      expect(dataFetcher).not.toHaveBeenCalledWith(REQUEST_TEMPLATE_RESULT);
+      expect(templates.response.render).not.toHaveBeenCalled();
+    });
+
+    it('should collect all the errors in context object', async () => {
+      templates.request.render.mockReturnValue({
+        ...REQUEST_TEMPLATE_RESULT,
+        errors: ['request error'],
+      });
+      templates.response.render.mockReturnValue({
+        ...REQUEST_TEMPLATE_RESULT,
+        errors: ['response error'],
+      });
+      const result = await resolver.resolve(source, args, context, info);
+      expect(result).toEqual(REQUEST_TEMPLATE_RESULT.result);
+      expect(context.appsyncErrors).toEqual(['request error', 'response error']);
+    });
+  });
+});
diff --git a/packages/amplify-appsync-simulator/src/resolvers/pipeline-resolver.ts b/packages/amplify-appsync-simulator/src/resolvers/pipeline-resolver.ts
index 4789cff3339..fcd7487bcc5 100644
--- a/packages/amplify-appsync-simulator/src/resolvers/pipeline-resolver.ts
+++ b/packages/amplify-appsync-simulator/src/resolvers/pipeline-resolver.ts
@@ -33,26 +33,22 @@ export class AppSyncPipelineResolver extends AppSyncBaseResolver {
       info,
     ));
 
-    context.appsyncErrors = [...context.appsyncErrors, ...templateErrors];
+    context.appsyncErrors = [...context.appsyncErrors, ...(templateErrors || [])];
 
     if (isReturn) {
       //Request mapping template called #return, don't process further
       return result;
     }
 
-    let prevResult;
+    let prevResult = result;
     for (let fnName of this.config.functions) {
       const fnResolver = this.simulatorContext.getFunction(fnName);
       ({ result: prevResult, stash } = await fnResolver.resolve(source, args, stash, prevResult, context, info));
     }
 
     // pipeline response mapping template
-    ({ result, errors: templateErrors } = responseMappingTemplate.render(
-      { source, arguments: args, result, prevResult, stash },
-      context,
-      info,
-    ));
-    context.appsyncErrors = [...context.appsyncErrors, ...templateErrors];
+    ({ result, errors: templateErrors } = responseMappingTemplate.render({ source, arguments: args, prevResult, stash }, context, info));
+    context.appsyncErrors = [...context.appsyncErrors, ...(templateErrors || [])];
     return result;
   }
 }