test: Test importance sampling with a model and constraints resulting…

… in samples with weight 0

This crashed previously.

test/gen/inference/importance_test.cljc

@@ -0,0 +1,23 @@
+(ns gen.inference.importance-test
+  (:require [clojure.test :refer [deftest is testing]]
+            [gen.choicemap :as choicemap :refer [choicemap get-value]]
+            [gen.distribution.commons-math :as dist]
+            [gen.dynamic :as dynamic :refer [gen]]
+            [gen.inference.importance :as importance]
+            [gen.trace :as trace]))
+
+(def model-causing-rejection-sampling
+  (gen
+    []
+    (if (dynamic/trace! :foo dist/bernoulli 0.5)
+      (dynamic/trace! :bar dist/bernoulli 1.0)
+      (dynamic/trace! :bar dist/bernoulli 0.0))))
+
+(deftest rejection
+  (testing "Robustness in the presence of importance samples with weight log(0)."
+    (is {:foo true :bar true}
+        ;; Needs a couple of samples to trigger previous bug here.
+        (-> (importance/resampling model-causing-rejection-sampling [] (choicemap {:bar true}) 10)
+            (:trace)
+            (trace/get-choices)
+            (get-value)))))