try PBT with coverage #2

list/list_test.go

@@ -6,6 +6,8 @@ import (
 	"testing"
 )
 
+/*
+
 func TestListLen(t *testing.T) {
 	assert.Equal(t, 0, Empty().Len(), "should insert at head")
 	assert.Equal(t, 1, Empty().Conj(1).Len(), "should insert at head")
@@ -39,26 +41,33 @@ func TestListRest(t *testing.T) {
 	assert.Equal(t, Empty(), Empty().Rest(), "should return rest sublist")
 	assert.Equal(t, Empty(), Empty().Rest().Rest(), "should return rest sublist")
 }
+*/
 
-// generative tests
-func ListLengthProperty(t *testing.T) {
+func intListGen() *rapid.Generator[IList] {
+	return rapid.Custom(func(t *rapid.T) IList {
 		myList := Empty()
-	expectedSized := 0
-	rapid.Check(t, func(t *rapid.T) {
 		t.Repeat(map[string]func(*rapid.T){
 			"conj": func(t *rapid.T) {
-				expectedSized += 1
 				myList = myList.Conj(rapid.Int().Draw(t, "el"))
 			},
-			"rest": func(t *rapid.T) {
-				if !myList.IsEmpty() {
-					expectedSized -= 1
-				}
-				myList = myList.Rest()
-			},
-			"": func(t *rapid.T) {
-				assert.Equal(t, myList.Len(), expectedSized, "must be equal")
-			},
 		})
+		return myList
+	})
+}
+
+// generative tests
+func TestConjIncreasesLength(t *testing.T) {
+	rapid.Check(t, func(t *rapid.T) {
+		myList := intListGen().Draw(t, "myList")
+		assert.Equal(t, myList.Len()+1, myList.Conj(42).Len())
+	})
+}
+
+func TestRestDecreasesLengthForNonEmptyList(t *testing.T) {
+	rapid.Check(t, func(t *rapid.T) {
+		myList := intListGen().Filter(func(l IList) bool {
+			return !l.IsEmpty()
+		}).Draw(t, "myList")
+		assert.Equal(t, myList.Len()-1, myList.Rest().Len())
 	})
 }