Add simple plot test

packages/squiggle-lang/__tests__/SquiggleLibrary/SquiggleLibrary_Plot_test.res

@@ -0,0 +1,17 @@
+open Jest
+open Reducer_TestHelpers
+
+describe("Plot Library", () => {
+  testEvalToBe(`Plot.dist({
+    show: [{
+      name: "normal",
+      value: normal(0, 1)
+    }, {
+      name: "lognormal", 
+      value: 1 to 2
+    }, {
+      name: "constant", 
+      value: 3
+    }]
+})`, "Ok(Plot showing normal,lognormal,constant)")
+})