added hash_pair test

Author: sampersand

test/typecheck/hash_pair/Steepfile

@@ -0,0 +1,7 @@
+D = Steep::Diagnostic
+
+target :test do
+  signature "."
+  check "."
+  configure_code_diagnostics(D::Ruby.all_error)
+end

test/typecheck/hash_pair/test.rb

@@ -0,0 +1,37 @@
+class ToAry
+  def initialize (*x) @x = x end
+  def to_ary = @x
+end
+
+class Pair
+  def initialize(x, y) @x, @y = x, y end
+  def to_ary = [@x, @y]
+end
+
+class Test
+  def self.takes_pair(pair)
+    x, y = pair.to_ary
+    x + y
+  end
+end
+
+is_pair = Pair.new(1, 2r) #: Pair[Integer, Rational]
+
+Test.takes_pair(is_pair)
+
+
+Hash[[
+  Pair.new(:a, 1r),
+  Pair.new(:b, 2r)
+]] #: Hash[Symbol, Rational]
+
+Hash[
+  ToAry.new(
+    Pair.new(:a, 1r),
+    Pair.new(:b, 2r)
+  )
+] #: Hash[Symbol, Rational]
+
+hash = { a: 3, b: 4 }
+hash.to_h { |k, v| Pair.new(k.to_s, v.to_r) } #: Hash[String, Rational]
+

test/typecheck/hash_pair/test.rbs

@@ -0,0 +1,18 @@
+class ToAry[X]
+  @x: Array[X]
+  def initialize: (*X) -> void
+  def to_ary: () -> Array[X]
+end
+
+class Pair[X, Y]
+  @x: X
+  @y: Y
+
+  def initialize: (X, Y) -> void
+
+  def to_ary: () -> [X, Y]
+end
+
+class Test
+  def self.takes_pair: (Hash::_Pair[Integer, Rational]) -> Rational
+end