fix(docdb): autoMinorVersionUpgrade property was not set to true …

…by default as stated in the docstring (#9505)

Fixes #9494

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

packages/@aws-cdk/aws-docdb/lib/instance.ts

@@ -203,7 +203,7 @@ export class DatabaseInstance extends DatabaseInstanceBase implements IDatabaseI
     const instance = new CfnDBInstance(this, 'Resource', {
       dbClusterIdentifier: props.cluster.clusterIdentifier,
       dbInstanceClass: `db.${props.instanceClass}`,
-      autoMinorVersionUpgrade: props.autoMinorVersionUpgrade,
+      autoMinorVersionUpgrade: props.autoMinorVersionUpgrade ?? true,
       availabilityZone: props.availabilityZone,
       dbInstanceIdentifier: props.dbInstanceName,
       preferredMaintenanceWindow: props.preferredMaintenanceWindow,

packages/@aws-cdk/aws-docdb/test/instance.test.ts

@@ -24,6 +24,34 @@ describe('DatabaseInstance', () => {
       Properties: {
         DBClusterIdentifier: { Ref: 'DatabaseB269D8BB' },
         DBInstanceClass: EXPECTED_SYNTH_INSTANCE_TYPE,
+        AutoMinorVersionUpgrade: true,
+      },
+      DeletionPolicy: 'Retain',
+      UpdateReplacePolicy: 'Retain',
+    }, ResourcePart.CompleteDefinition));
+  });
+
+  test.each([
+    [undefined, true],
+    [true, true],
+    [false, false],
+  ])('check that autoMinorVersionUpdate works: %p', (given: boolean | undefined, expected: boolean) => {
+    // GIVEN
+    const stack = testStack();
+
+    // WHEN
+    new DatabaseInstance(stack, 'Instance', {
+      cluster: stack.cluster,
+      instanceClass: SINGLE_INSTANCE_TYPE,
+      autoMinorVersionUpgrade: given,
+    });
+
+    // THEN
+    expectCDK(stack).to(haveResource('AWS::DocDB::DBInstance', {
+      Properties: {
+        DBClusterIdentifier: { Ref: 'DatabaseB269D8BB' },
+        DBInstanceClass: EXPECTED_SYNTH_INSTANCE_TYPE,
+        AutoMinorVersionUpgrade: expected,
       },
       DeletionPolicy: 'Retain',
       UpdateReplacePolicy: 'Retain',