fix: add test for Fix1

Author: Nimrais

test/interface/fix1_tests.jl

@@ -0,0 +1,12 @@
+@testitem "Support ::Base.Fix1{typeof(logpdf), D}" begin
+    using Distributions
+    using ClosedFormExpectations
+    using StableRNGs
+    using Base.MathConstants: eulergamma
+
+    include("../test_utils.jl")
+    rng = StableRNG(123)
+    dist = Exponential(1.0)
+    fixed_logpdf = Base.Fix1(logpdf, dist)
+    @test mean(ClosedFormExpectation(), fixed_logpdf, Exponential(10.0)) ≈ mean(ClosedFormExpectation(), Logpdf(Exponential(1.0)), Exponential(10.0))
+end