diff --git a/spec/test-data.cr b/spec/test-data.cr
new file mode 100644
index 0000000..2df42ed
--- /dev/null
+++ b/spec/test-data.cr
@@ -0,0 +1,87 @@
+require "uuid"
+require "json"
+
+# FIXME: Split the test data in separate files. We don’t care about those here.
+
+class Ship
+	include JSON::Serializable
+
+	def_clone
+
+	property id    : String
+	property klass : String
+	property name  : String
+	property tags  : Array(String)
+
+	def initialize(@name, @klass = "<unknown>", @id = UUID.random.to_s, @tags = [] of String)
+	end
+
+	# Makes testing arrays of this class easier.
+	def <=>(other)
+		@name <=> other.name
+	end
+
+	# Common, reusable test data.
+	# Those data can be indexed, partitioned or tagged on different parameters,
+	# and can easily be extended.
+
+	class_getter kisaragi = Ship.new("Kisaragi", "Mutsuki")
+	class_getter mutsuki  = Ship.new("Mutsuki",  "Mutsuki", tags: ["name ship"])
+	class_getter yayoi    = Ship.new("Yayoi",    "Mutsuki")
+	class_getter destroyers = [
+		@@mutsuki,
+		@@kisaragi,
+		@@yayoi,
+		Ship.new("Uzuki",    "Mutsuki"),
+		Ship.new("Satsuki",  "Mutsuki"),
+
+		Ship.new("Shiratsuyu", "Shiratsuyu", tags: ["name ship"]),
+		Ship.new("Murasame",   "Shiratsuyu"),
+		Ship.new("Yuudachi",   "Shiratsuyu")
+	]
+
+	class_getter yamato = 
+		Ship.new("Yamato",    "Yamato",      tags: ["name ship", "flagship"])
+	class_getter flagship : Ship = yamato
+	class_getter battleships = [
+		@@yamato,
+		Ship.new("Kongou",    "Kongou",      tags: ["name ship"]),
+		Ship.new("Haruna",    "Kongou"),
+		Ship.new("Kirishima", "Kongou"),
+		Ship.new("Hiei"     , "Kongou"),
+		Ship.new("Musashi",   "Yamato"),
+		Ship.new("Shinano",   "Yamato")
+	]
+
+	class_getter all_ships : Array(Ship) = @@destroyers + @@battleships
+
+	# Equality is true if every property is identical.
+	def ==(other)
+		@id == other.id && @klass == other.klass && @name == other.name &&
+			@tags == other.tags
+	end
+end
+
+# This will be used for migration testing, but basically it’s a variant of
+# the class above, a few extra fields, a few missing ones.
+class PrimitiveShip
+	include JSON::Serializable
+
+	property id         : String
+	property name       : String
+	property wooden     : Bool   = false # Will be removed.
+	property class_name : String         # Will be renamed
+	property flagship   : Bool   = false # Will be moved to tags.
+
+	def initialize(@name, @class_name = "<unknown>", @id = UUID.random.to_s, @flagship = false)
+	end
+
+	class_getter kamikaze =
+		PrimitiveShip.new("Kamikaze", "Kamikaze")
+	class_getter asakaze =
+		PrimitiveShip.new("Asakaze",  "Kamikaze")
+	class_getter all_ships : Array(PrimitiveShip) = [
+		@@kamikaze,
+		@@asakaze
+	]
+end