Add a crash test to mono

crates/compiler/test_mono/generated/crash.txt

@@ -0,0 +1,18 @@
+procedure Test.1 (Test.2):
+    let Test.10 : U8 = 1i64;
+    let Test.11 : U8 = GetTagId Test.2;
+    let Test.12 : Int1 = lowlevel Eq Test.10 Test.11;
+    if Test.12 then
+        let Test.3 : U64 = UnionAtIndex (Id 1) (Index 0) Test.2;
+        dec Test.2;
+        ret Test.3;
+    else
+        dec Test.2;
+        let Test.9 : Str = "turns out this was fallible";
+        Crash `#UserApp.9`
+
+procedure Test.0 ():
+    let Test.13 : U64 = 78i64;
+    let Test.4 : [C Str, C U64] = TagId(1) Test.13;
+    let Test.6 : U64 = CallByName Test.1 Test.4;
+    ret Test.6;

crates/compiler/test_mono/src/tests.rs

@@ -2035,11 +2035,16 @@ fn recursive_function_and_union_with_inference_hole() {
 fn crash() {
     indoc!(
         r#"
-        app "test" provides [getInfallible] to "./platform"
+        app "test" provides [main] to "./platform"
 
         getInfallible = \result -> when result is
             Ok x -> x
             _ -> crash "turns out this was fallible"
+
+        main =
+            x : [Ok U64, Err Str]
+            x = Ok 78
+            getInfallible x
         "#
     )
 }