add mutators.None predicate

README.md

@@ -197,14 +197,15 @@ To help construct more complex yet readable predicates easily, **govcr** provide
 - `Any` achieves a logical "**or**" of the provided predicates.
 - `All` achieves a logical "**and**" of the provided predicates.
 - `Not` achieves a logical "**not**" of the provided predicates.
+- `None` is synonymous of "`Not` `Any`".
 
 Examples:
 
 ```go
 myMutator.
     On(Any(...)). // proceeds if any of the "`...`" predicates is true
     On(Not(Any(...)))  // proceeds if none of the "`...`" predicates is true (i.e. all predicates are false)
-    On(Not(All(...))).  // proceeds if not every of the "`...`" predicates is true (i.e. at least one predicate is false)
+    On(Not(All(...))).  // proceeds if not every (including none) of the "`...`" predicates is true (i.e. at least one predicate is false, possibly all of them).
 ```
 
 A **track recording mutator** can change both the request and the response that will be persisted to the cassette.

cassette/track/mutator.go

@@ -41,6 +41,12 @@ func All(predicates ...Predicate) Predicate {
 	)
 }
 
+// None requires all predicates to be false.
+// I.e. it is the equivalent of Not(Any(...)).
+func None(predicates ...Predicate) Predicate {
+	return Not(Any(predicates...))
+}
+
 // Not accepts one predicate and returns its logically contrary evaluation.
 // I.e. it returns true when the supplied predicate is false and vice-versa.
 func Not(predicate Predicate) Predicate {

cassette/track/mutator_test.go

@@ -83,6 +83,34 @@ func Test_Mutator_Any(t *testing.T) {
 	require.True(t, result)
 }
 
+func Test_Mutator_None(t *testing.T) {
+	pTrue := track.Predicate(
+		func(trk *track.Track) bool {
+			return true
+		},
+	)
+
+	pFalse := track.Predicate(
+		func(trk *track.Track) bool {
+			return false
+		},
+	)
+
+	trk := track.NewTrack(nil, nil, nil)
+
+	result := track.None(pFalse, pTrue)(nil)
+	require.False(t, result)
+
+	result = track.None(pFalse, pTrue)(trk)
+	require.False(t, result)
+
+	result = track.None(pFalse, pFalse)(trk)
+	require.True(t, result)
+
+	result = track.None(pTrue, pTrue)(trk)
+	require.False(t, result)
+}
+
 func Test_Mutator_All(t *testing.T) {
 	pTrue := track.Predicate(
 		func(trk *track.Track) bool {