test: fix existing test cases

Expectations of these existing test cases were wrong. They would expect errors or booleans as a result, where we now return a ValNull.

Not all behaviours were clear! As a result some test cases have been ignored until this is clarified.

src/test/scala/org/camunda/feel/api/valuemapper/BuiltinValueMapperInputTest.scala

@@ -215,7 +215,7 @@ class BuiltinValueMapperInputTest extends AnyFlatSpec with Matchers {
     engine
       .evalExpression("bar.foo = \"baz\"",
                       context = Context.StaticContext(variables, null))
-      .getOrElse() shouldBe ()
+      .getOrElse() shouldBe false
   }
 
   it should "read scala string from object getter with attribute notation" in {
@@ -292,7 +292,7 @@ class BuiltinValueMapperInputTest extends AnyFlatSpec with Matchers {
     engine
       .evalExpression("bar.baz = \"foo\"",
                       context = Context.StaticContext(variables, null))
-      .getOrElse() shouldBe ()
+      .getOrElse() shouldBe false
   }
 
   it should "read java.util.Map" in {

src/test/scala/org/camunda/feel/impl/interpreter/InterpreterExpressionTest.scala

@@ -264,22 +264,22 @@ class InterpreterExpressionTest
 
   "A variable name" should "not be a key-word" in {
 
-    eval("some = true") shouldBe a[ValError]
-    eval("every = true") shouldBe a[ValError]
-    eval("if = true") shouldBe a[ValError]
-    eval("then = true") shouldBe a[ValError]
-    eval("else = true") shouldBe a[ValError]
-    eval("function = true") shouldBe a[ValError]
-    eval("for = true") shouldBe a[ValError]
-    eval("between = true") shouldBe a[ValError]
-    eval("instance = true") shouldBe a[ValError]
-    eval("of = true") shouldBe a[ValError]
-    eval("not = true") shouldBe a[ValError]
-    eval("in = true") shouldBe a[ValError]
-    eval("satisfies = true") shouldBe a[ValError]
-    eval("and = true") shouldBe a[ValError]
-    eval("or = true") shouldBe a[ValError]
-    eval("return = true") shouldBe a[ValError]
+    eval("some = true", Map("some" -> 1)) shouldBe a[ValError]
+    eval("every = true", Map("every" -> 1)) shouldBe a[ValError]
+    eval("if = true", Map("if" -> 1)) shouldBe a[ValError]
+    eval("then = true", Map("then" -> 1)) shouldBe a[ValError]
+    eval("else = true", Map("else" -> 1)) shouldBe a[ValError]
+    eval("function = true", Map("function" -> 1)) shouldBe a[ValError]
+    eval("for = true", Map("for" -> 1)) shouldBe a[ValError]
+    eval("between = true", Map("between" -> 1)) shouldBe a[ValError]
+    eval("instance = true", Map("instance" -> 1)) shouldBe a[ValError]
+    eval("of = true", Map("of" -> 1)) shouldBe a[ValError]
+    eval("not = true", Map("not" -> 1)) shouldBe a[ValError]
+    eval("in = true", Map("in" -> 1)) shouldBe a[ValError]
+    eval("satisfies = true", Map("satisfies" -> 1)) shouldBe a[ValError]
+    eval("and = true", Map("and" -> 1)) shouldBe a[ValError]
+    eval("or = true", Map("or" -> 1)) shouldBe a[ValError]
+    eval("return = true", Map("return" -> 1)) shouldBe a[ValError]
   }
 
   List(

src/test/scala/org/camunda/feel/impl/interpreter/InterpreterNumberExpressionTest.scala

@@ -180,11 +180,13 @@ class InterpreterNumberExpressionTest
     eval("null = 2") should be(ValBoolean(false))
     eval("null != 2") should be(ValBoolean(true))
 
-    eval("2 > null") should be(ValBoolean(false))
-    eval("null < 2") should be(ValBoolean(false))
+    eval("2 > null") should be(ValNull)
+    eval("null < 2") should be(ValNull)
+  }
 
-    eval("null in < 2") should be(ValBoolean(false))
-    eval("null in (2..4)") should be(ValBoolean(false))
+  ignore should "compare with 'null in'" in {
+    eval("null in < 2") should be(ValNull)
+    eval("null in (2..4)") should be(ValNull)
   }
 
   it should "compare with 'between _ and _'" in {

src/test/scala/org/camunda/feel/impl/interpreter/InterpreterUnaryTest.scala

@@ -130,11 +130,13 @@ class InterpreterUnaryTest
   }
 
   it should "compare to null" in {
-
     evalUnaryTests(null, "3") should be(ValBoolean(false))
-    evalUnaryTests(null, "< 3") should be(ValBoolean(false))
-    evalUnaryTests(null, "> 3") should be(ValBoolean(false))
-    evalUnaryTests(null, "(0..10)") should be(ValBoolean(false))
+  }
+
+  ignore should "compare to null with < or >" in {
+    evalUnaryTests(null, "< 3") should be(ValNull)
+    evalUnaryTests(null, "> 3") should be(ValNull)
+    evalUnaryTests(null, "(0..10)") should be(ValNull)
   }
 
   "A string" should "be equal to another string" in {