PBT all the things

list/list_test.go

@@ -9,6 +9,7 @@ import (
 	"pgregory.net/rapid"
 )
 
+// intListGen returns a generator for either empty list or random ints
 func intListGen() *rapid.Generator[IList] {
 	return rapid.OneOf(rapid.Custom(func(t *rapid.T) IList {
 		myList := Empty()
@@ -21,22 +22,20 @@ func intListGen() *rapid.Generator[IList] {
 	}), rapid.Just(Empty()))
 }
 
-func TestConjIncreasesLength(t *testing.T) {
-	rapid.Check(t, func(t *rapid.T) {
-		myList := intListGen().Draw(t, "myList")
-		newElem := rapid.Int().Draw(t, "newElem")
-		assert.Equal(t, myList.Len()+1, myList.Conj(newElem).Len(), "conj increases length")
-	})
-}
-
-func TestRestDecreasesLength(t *testing.T) {
-	rapid.Check(t, func(t *rapid.T) {
-		myList := intListGen().Draw(t, "myList")
-		if myList.IsEmpty() {
-			assert.Equal(t, myList.Len(), myList.Rest().Len(), "rest does not change length for empty list")
-		} else {
-			assert.Equal(t, myList.Len()-1, myList.Rest().Len(), "rest decreases length of non-empty list")
-		}
+// descSortedIntListGen returns a generator for list of at least several descending ints
+func descSortedIntListGen() *rapid.Generator[IList] {
+	return rapid.Custom(func(t *rapid.T) IList {
+		myList := New(0)
+		i := 1
+		t.Repeat(map[string]func(*rapid.T){
+			"conj": func(t *rapid.T) {
+				myList = myList.Conj(i)
+				i += 1
+			},
+		})
+		return myList
+	}).Filter(func(l IList) bool {
+		return l.Len() > 1
 	})
 }
 
@@ -49,6 +48,32 @@ func TestFirstIsNilOnlyWhenEmpty(t *testing.T) {
 	})
 }
 
+func TestConj(t *testing.T) {
+	rapid.Check(t, func(t *rapid.T) {
+		myList := intListGen().Draw(t, "myList")
+		newElem := rapid.Int().Draw(t, "newElem")
+		myList2 := myList.Conj(newElem)
+		assert.Equal(t, myList.Len()+1, myList2.Len(), "conj increases length")
+		assert.Equal(t, newElem, myList2.First(), "first after conj returns inserted number")
+	})
+}
+
+func TestRest(t *testing.T) {
+	rapid.Check(t, func(t *rapid.T) {
+		myList := intListGen().Draw(t, "myList")
+		if myList.IsEmpty() {
+			assert.Equal(t, myList.Len(), myList.Rest().Len(), "rest does not change length for empty list")
+		} else {
+			assert.Equal(t, myList.Len()-1, myList.Rest().Len(), "rest decreases length of non-empty list")
+		}
+	})
+
+	rapid.Check(t, func(t *rapid.T) {
+		myList := descSortedIntListGen().Draw(t, "myList")
+		assert.GreaterOrEqual(t, myList.First(), myList.Rest().First(), "rest decreases value in list head")
+	})
+}
+
 func TestStringifyIntList(t *testing.T) {
 	assert.Equal(t, "(1 2 3)", New(3).Conj(2).Conj(1).String())
 
@@ -56,7 +81,7 @@ func TestStringifyIntList(t *testing.T) {
 		myList := intListGen().Draw(t, "myList")
 		s := myList.String()
 		r := regexp.MustCompile(`^\([\d\s-]*\)$`)
-		assert.Equal(t, true, r.Match([]byte(s)), s + " looks like a stringfied list")
+		assert.Equal(t, true, r.Match([]byte(s)), s+" looks like a stringified list")
 		if !myList.IsEmpty() {
 			assert.Equal(t, myList.Len(), strings.Count(s, " ")+1, "number of spaces in string should match count of elements")
 		} else {