diff --git a/drivers/place/at_capacity_mailer.cr b/drivers/place/at_capacity_mailer.cr
index aa9beb135a..cdcd9833ac 100644
--- a/drivers/place/at_capacity_mailer.cr
+++ b/drivers/place/at_capacity_mailer.cr
@@ -84,9 +84,9 @@ class Place::AtCapacityMailer < PlaceOS::Driver
     booked_asset_ids = get_booked_asset_ids
 
     @zones.each do |zone_id|
-      next if asset_ids[zone_id].empty?
+      next unless (zone_asset_ids = asset_ids[zone_id]?) && !zone_asset_ids.empty?
 
-      if (asset_ids[zone_id] - [booked_asset_ids]).empty?
+      if (zone_asset_ids - booked_asset_ids).empty?
         logger.debug { "zone #{zone_id} is at capacity" }
         send_email(zone_id)
       end
@@ -97,20 +97,16 @@ class Place::AtCapacityMailer < PlaceOS::Driver
     assets_ids = {} of String => Array(String)
 
     @zones.each do |zone_id|
-      begin
-        assets_ids[zone_id] = get_assets_from_metadata(@booking_type, zone_id).map { |asset| asset.id }.uniq!
-      rescue error
-        logger.warn(exception: error) { "unable to get #{@booking_type} assets from zone #{zone_id} metadata" }
-      end
+      assets_ids[zone_id] = get_assets_from_metadata(zone_id).map { |asset| asset.id }.uniq!
     end
 
     self[:assets_ids] = assets_ids
   end
 
-  def get_assets_from_metadata(type : String, zone_id : String) : Array(Asset)
+  def get_assets_from_metadata(zone_id : String) : Array(Asset)
     assets = [] of Asset
 
-    metadata_field = case type
+    metadata_field = case @booking_type
                      when "desk"
                        "desks"
                      when "parking"
@@ -121,16 +117,12 @@ class Place::AtCapacityMailer < PlaceOS::Driver
 
     if metadata_field
       metadata = Metadata.from_json staff_api.metadata(zone_id, metadata_field).get[metadata_field].to_json
-      if "lockers"
-        assets = metadata.details.as_a.flat_map { |locker_bank| locker_bank.as_h["lockers"].as_a.map { |locker| Asset.from_json locker.to_json } }
-      else
-        assets = metadata.details.as_a.map { |asset| Asset.from_json asset.to_json }
-      end
+      assets = metadata.details.as_a.map { |asset| Asset.from_json asset.to_json }
     end
 
     assets
   rescue error
-    logger.warn(exception: error) { "unable to get #{type} assets from zone #{zone_id} metadata" }
+    logger.warn(exception: error) { "unable to get #{metadata_field} from zone #{zone_id} metadata" }
     [] of Asset
   end
 
diff --git a/drivers/place/at_capacity_mailer_spec.cr b/drivers/place/at_capacity_mailer_spec.cr
new file mode 100644
index 0000000000..9fcd6ce271
--- /dev/null
+++ b/drivers/place/at_capacity_mailer_spec.cr
@@ -0,0 +1,324 @@
+require "placeos-driver/spec"
+require "placeos-driver/interface/mailer"
+
+class StaffAPI < DriverSpecs::MockDriver
+  ZONES = [
+    {
+      created_at:   1660537814,
+      updated_at:   1681800971,
+      id:           "level-1",
+      name:         "Level 1",
+      display_name: "Level 1",
+      location:     "",
+      description:  "",
+      code:         "",
+      type:         "",
+      count:        0,
+      capacity:     0,
+      map_id:       "",
+      tags:         [
+        "level",
+      ],
+      triggers:  [] of String,
+      parent_id: "zone-0000",
+      timezone:  "Australia/Sydney",
+    },
+    {
+      created_at:   1660537814,
+      updated_at:   1681800971,
+      id:           "level-2",
+      name:         "Level 2",
+      display_name: "Level 2",
+      location:     "",
+      description:  "",
+      code:         "",
+      type:         "",
+      count:        0,
+      capacity:     0,
+      map_id:       "",
+      tags:         [
+        "level",
+      ],
+      triggers:  [] of String,
+      parent_id: "zone-0000",
+      timezone:  "Australia/Sydney",
+    },
+  ]
+
+  def zone(zone_id : String)
+    zones = ZONES.select { |z| z["id"] == zone_id }
+    JSON.parse(zones.to_json)
+  end
+
+  def metadata(id : String, key : String? = nil)
+    zone = ZONES.find! { |z| z["id"] == id }
+    key = key.not_nil!
+
+    details = case key
+              when "desks"
+                [
+                  {
+                    "id":       "desk-1",
+                    "name":     "Desk 1",
+                    "images":   [] of String,
+                    "bookable": true,
+                    "features": [] of String,
+                  },
+                  {
+                    "id":       "desk-2",
+                    "name":     "Desk 2",
+                    "images":   [] of String,
+                    "bookable": true,
+                    "features": [] of String,
+                  },
+                ]
+              when "parking-spaces"
+                [
+                  {
+                    "id":            "park-1",
+                    "name":          "Bay 1",
+                    "zone":          zone[:id],
+                    "notes":         "",
+                    "map_id":        "",
+                    "zone_id":       zone[:id],
+                    "assigned_to":   nil,
+                    "map_rotation":  0,
+                    "assigned_name": nil,
+                    "assigned_user": nil,
+                  },
+                  {
+                    "id":            "park-2",
+                    "name":          "Bay 2",
+                    "zone":          zone[:id],
+                    "notes":         "",
+                    "map_id":        "",
+                    "zone_id":       zone[:id],
+                    "assigned_to":   nil,
+                    "map_rotation":  0,
+                    "assigned_name": nil,
+                    "assigned_user": nil,
+                  },
+                ]
+              when "lockers"
+                [
+                  {
+                    "id":   "locker-1",
+                    "name": "L1-01",
+                    "size": [
+                      1,
+                      3,
+                    ],
+                    "tags": [
+                      "Base",
+                    ],
+                    "notes":    "",
+                    "bank_id":  "bank-1",
+                    "bookable": true,
+                    "features": [] of String,
+                    "position": [
+                      0,
+                      0,
+                    ],
+                    "accessible":    true,
+                    "assigned_user": nil,
+                  },
+                  {
+                    "id":   "locker-2",
+                    "name": "L1-02",
+                    "size": [
+                      1,
+                      3,
+                    ],
+                    "tags": [
+                      "Base",
+                    ],
+                    "notes":    "",
+                    "bank_id":  "bank-1",
+                    "bookable": true,
+                    "features": [] of String,
+                    "position": [
+                      1,
+                      0,
+                    ],
+                    "accessible":    true,
+                    "assigned_user": nil,
+                  },
+                ]
+              end
+
+    JSON.parse(
+      {key => {
+        name:           key,
+        description:    "#{key} for zone #{id}",
+        details:        details,
+        parent_id:      zone[:parent_id],
+        editors:        [] of String,
+        modified_by_id: "user-1234",
+      }}.to_json)
+  end
+
+  def booked(
+    type : String? = nil,
+    period_start : Int64? = nil,
+    period_end : Int64? = nil,
+    zones : Array(String) = [] of String,
+    user : String? = nil,
+    email : String? = nil,
+    state : String? = nil,
+    event_id : String? = nil,
+    ical_uid : String? = nil,
+    created_before : Int64? = nil,
+    created_after : Int64? = nil,
+    approved : Bool? = nil,
+    checked_in : Bool? = nil,
+    include_checked_out : Bool? = nil,
+    include_booked_by : Bool? = nil,
+    department : String? = nil,
+    limit : Int32? = nil,
+    offset : Int32? = nil,
+    permission : String? = nil,
+    extension_data : JSON::Any? = nil,
+  )
+    assets = case type
+             when "desk"
+               ["desk-1", "desk-2"]
+             when "parking"
+               ["park-1"]
+             when "locker"
+               ["locker-1", "locker-2"]
+             end
+    JSON.parse(assets.to_json)
+  end
+end
+
+class Mailer < DriverSpecs::MockDriver
+  include PlaceOS::Driver::Interface::Mailer
+
+  def on_load
+    self[:sent] = 0
+  end
+
+  def send_template(
+    to : String | Array(String),
+    template : Tuple(String, String),
+    args : TemplateItems,
+    resource_attachments : Array(ResourceAttachment) = [] of ResourceAttachment,
+    attachments : Array(Attachment) = [] of Attachment,
+    cc : String | Array(String) = [] of String,
+    bcc : String | Array(String) = [] of String,
+    from : String | Array(String) | Nil = nil,
+    reply_to : String | Array(String) | Nil = nil
+  )
+    self[:sent] = self[:sent].as_i + 1
+  end
+
+  def send_mail(
+    to : String | Array(String),
+    subject : String,
+    message_plaintext : String? = nil,
+    message_html : String? = nil,
+    resource_attachments : Array(ResourceAttachment) = [] of ResourceAttachment,
+    attachments : Array(Attachment) = [] of Attachment,
+    cc : String | Array(String) = [] of String,
+    bcc : String | Array(String) = [] of String,
+    from : String | Array(String) | Nil = nil,
+    reply_to : String | Array(String) | Nil = nil
+  ) : Bool
+    true
+  end
+end
+
+DriverSpecs.mock_driver "Place::AtCapacityMailer" do
+  system({
+    StaffAPI: {StaffAPI},
+    Mailer:   {Mailer},
+  })
+
+  # Start of tests for: #get_booked_asset_ids
+  ###########################################
+
+  settings({
+    booking_type: "parking",
+    zones:        ["level-1"],
+  })
+
+  resp = exec(:get_booked_asset_ids).get
+  resp.not_nil!.as_a.should eq ["park-1"]
+
+  ###########################################
+  # End of tests for: #get_booked_asset_ids
+
+  # Start of tests for: #get_assets_from_metadata
+  ###############################################
+
+  settings({
+    booking_type: "desk",
+    zones:        ["level-1"],
+  })
+
+  resp = exec(:get_assets_from_metadata, "level-1").get
+  resp.not_nil!.as_a.map(&.as_h["id"]).should eq ["desk-1", "desk-2"]
+
+  settings({
+    booking_type: "parking",
+    zones:        ["level-1"],
+  })
+
+  resp = exec(:get_assets_from_metadata, "level-1").get
+  resp.not_nil!.as_a.map(&.as_h["id"]).should eq ["park-1", "park-2"]
+
+  settings({
+    booking_type: "locker",
+    zones:        ["level-1"],
+  })
+
+  resp = exec(:get_assets_from_metadata, "level-1").get
+  resp.not_nil!.as_a.map(&.as_h["id"]).should eq ["locker-1", "locker-2"]
+
+  ###############################################
+  # End of tests for: #get_assets_from_metadata
+
+  # Start of tests for: #get_asset_ids
+  ####################################
+
+  settings({
+    booking_type: "desk",
+    zones:        ["level-1"],
+  })
+
+  resp = exec(:get_asset_ids).get
+  resp.not_nil!.as_h.should eq Hash{"level-1" => ["desk-1", "desk-2"]}
+
+  ####################################
+  # End of tests for: #get_asset_ids
+
+  # Start of tests for: #check_capacity
+  #####################################
+
+  # Not fully booked
+  settings({
+    booking_type: "parking",
+    zones:        ["level-1"],
+  })
+  _resp = exec(:get_asset_ids).get # asset_ids are cached
+
+  resp = exec(:check_capacity).get
+  system(:Mailer_1)[:sent].should eq 0
+
+  #  Fully booked
+  settings({
+    booking_type: "locker",
+    zones:        ["level-1"],
+  })
+  _resp = exec(:get_asset_ids).get # asset_ids are cached
+
+  resp = exec(:check_capacity).get
+  system(:Mailer_1)[:sent].should eq 1
+
+  # spam protection
+  resp = exec(:check_capacity).get
+  system(:Mailer_1)[:sent].should eq 1
+
+  #####################################
+  # End of tests for: #check_capacity
+end