chore: use non-deprecated Lambda runtime in unit tests [skip ci] (#408)

No tangible difference, just addresses deprecation warnings.

---

_By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache-2.0 license_

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Author: Eugene Cheung

test/dashboard/widget/CustomWidget.test.ts

@@ -8,7 +8,7 @@ test("widget", () => {
 
   const handler = new Function(stack, "Function", {
     // execution environment
-    runtime: Runtime.NODEJS_12_X,
+    runtime: Runtime.NODEJS_18_X,
     // code loaded from "lambda" directory
     code: Code.fromInline(
       'exports.handler = function(event, ctx, cb) { return cb(null, "Hello World!"); }'

test/facade/MonitoringAspect.test.ts

@@ -391,7 +391,7 @@ describe("MonitoringAspect", () => {
     new lambda.Function(stack, "DummyFunction", {
       code: lambda.Code.fromInline("lambda"),
       handler: "index.handler",
-      runtime: lambda.Runtime.NODEJS_12_X,
+      runtime: lambda.Runtime.NODEJS_18_X,
     });
 
     // WHEN

test/facade/__snapshots__/MonitoringAspect.test.ts.snap

@@ -19,7 +19,7 @@ test("snapshot test: no alarms", () => {
 
   const lambdaFunction = new Function(stack, "Function", {
     functionName: "DummyLambda",
-    runtime: Runtime.NODEJS_12_X,
+    runtime: Runtime.NODEJS_18_X,
     code: InlineCode.fromInline("{}"),
     handler: "Dummy::handler",
   });
@@ -49,7 +49,7 @@ test("snapshot test: all alarms", () => {
 
   const lambdaFunction = new Function(stack, "Function", {
     functionName: "DummyLambda",
-    runtime: Runtime.NODEJS_12_X,
+    runtime: Runtime.NODEJS_18_X,
     code: InlineCode.fromInline("{}"),
     handler: "Dummy::handler",
   });
@@ -156,7 +156,7 @@ test("snapshot test: all alarms", () => {
 
   const lambdaFunction = new Function(stack, "Function", {
     functionName: "DummyLambda",
-    runtime: Runtime.NODEJS_12_X,
+    runtime: Runtime.NODEJS_18_X,
     code: InlineCode.fromInline("{}"),
     handler: "Dummy::handler",
     layers: [
@@ -196,7 +196,7 @@ test("snapshot test: all alarms, alarmPrefix on error dedupeString", () => {
 
   const lambdaFunction = new Function(stack, "Function", {
     functionName: "DummyLambda",
-    runtime: Runtime.NODEJS_12_X,
+    runtime: Runtime.NODEJS_18_X,
     code: InlineCode.fromInline("{}"),
     handler: "Dummy::handler",
   });
@@ -334,7 +334,7 @@ test("snapshot test: all alarms, alarmPrefix on latency dedupeString", () => {
 
   const lambdaFunction = new Function(stack, "Function", {
     functionName: "DummyLambda",
-    runtime: Runtime.NODEJS_12_X,
+    runtime: Runtime.NODEJS_18_X,
     code: InlineCode.fromInline("{}"),
     handler: "Dummy::handler",
   });
@@ -472,7 +472,7 @@ test("doesn't create alarms for enhanced Lambda Insights metrics if not enabled"
 
   const lambdaFunction = new Function(stack, "Function", {
     functionName: "DummyLambda",
-    runtime: Runtime.NODEJS_12_X,
+    runtime: Runtime.NODEJS_18_X,
     code: InlineCode.fromInline("{}"),
     handler: "Dummy::handler",
   });

test/monitoring/aws-lambda/LambdaFunctionMonitoring.test.ts

@@ -16,7 +16,7 @@ test("snapshot test: no alarms", () => {
 
   const lambdaFunction = new Function(stack, "Function", {
     functionName: "DummyLambda",
-    runtime: Runtime.NODEJS_12_X,
+    runtime: Runtime.NODEJS_18_X,
     code: InlineCode.fromInline("{}"),
     handler: "Dummy::handler",
   });
@@ -37,7 +37,7 @@ test("snapshot test: all alarms", () => {
 
   const lambdaFunction = new Function(stack, "Function", {
     functionName: "DummyLambda",
-    runtime: Runtime.NODEJS_12_X,
+    runtime: Runtime.NODEJS_18_X,
     code: InlineCode.fromInline("{}"),
     handler: "Dummy::handler",
   });