add test for regularity

golden-tests/tests/regularity/expected

@@ -0,0 +1 @@
+0.reggie : 1.(A : ★) → 1.(AA : A ≡ A : ★) → 1.(s : A) → 1.(P : 1.A → ★) → 1.(P (coe (𝑖 ⇒ AA @𝑖) @0 @1 s)) → P s

golden-tests/tests/regularity/regularity.quox

@@ -0,0 +1,12 @@
+-- this definition depends on coercion regularity in xtt. which is this
+-- (adapted to quox):
+--
+--           Ψ | Γ ⊢ 0 · A‹0/𝑖› = A‹1/𝑖› ⇐ ★
+-- ---------------------------------------------------------
+--  Ψ | Γ ⊢ π · coe (𝑖 ⇒ A) @p @q s ⇝ (s ∷ A‹1/𝑖›) ⇒ A‹1/𝑖›
+--
+-- otherwise, the types P (coe ⋯ s) and P s are incompatible
+
+def0 reggie : (A : ★) → (AA : A ≡ A : ★) → (s : A) →
+              (P : A → ★) → P (coe (𝑖 ⇒ AA @𝑖) s) → P s =
+  λ A AA s P p ⇒ p

golden-tests/tests/regularity/run

@@ -0,0 +1,2 @@
+. ../lib.sh
+check "$1" regularity.quox