Correct response when trying to delete a volume that is attached to an EC2 instance. Created a VolumeInUse error and did a simple check on the delete_volume method.

moto/ec2/exceptions.py

@@ -244,6 +244,15 @@ class InvalidVolumeAttachmentError(EC2ClientError):
             .format(volume_id, instance_id))
 
 
+class VolumeInUseError(EC2ClientError):
+
+    def __init__(self, volume_id, instance_id):
+        super(VolumeInUseError, self).__init__(
+            "VolumeInUse",
+            "Volume {0} is currently attached to {1}"
+            .format(volume_id, instance_id))
+
+
 class InvalidDomainError(EC2ClientError):
 
     def __init__(self, domain):

moto/ec2/models.py

@@ -45,6 +45,7 @@ from .exceptions import (
     InvalidAMIAttributeItemValueError,
     InvalidSnapshotIdError,
     InvalidVolumeIdError,
+    VolumeInUseError,
     InvalidVolumeAttachmentError,
     InvalidDomainError,
     InvalidAddressError,
@@ -1813,6 +1814,10 @@ class EBSBackend(object):
 
     def delete_volume(self, volume_id):
         if volume_id in self.volumes:
+            volume = self.volumes[volume_id]
+            instance_id = volume.attachment.instance.id
+            if volume.attachment is not None:
+                raise VolumeInUseError(volume_id, instance_id)
             return self.volumes.pop(volume_id)
         raise InvalidVolumeIdError(volume_id)