Merge pull request #1129 from palsivertsen/not-error-as

Add assertion for NotErrorAs

assert/assertions.go

@@ -2149,6 +2149,24 @@ func ErrorAs(t TestingT, err error, target interface{}, msgAndArgs ...interface{
 	), msgAndArgs...)
 }
 
+// NotErrorAs asserts that none of the errors in err's chain matches target,
+// but if so, sets target to that error value.
+func NotErrorAs(t TestingT, err error, target interface{}, msgAndArgs ...interface{}) bool {
+	if h, ok := t.(tHelper); ok {
+		h.Helper()
+	}
+	if !errors.As(err, target) {
+		return true
+	}
+
+	chain := buildErrorChainString(err)
+
+	return Fail(t, fmt.Sprintf("Target error should not be in err chain:\n"+
+		"found: %q\n"+
+		"in chain: %s", target, chain,
+	), msgAndArgs...)
+}
+
 func buildErrorChainString(err error) string {
 	if err == nil {
 		return ""

assert/assertions_test.go

@@ -3269,7 +3269,6 @@ func TestNotErrorIs(t *testing.T) {
 }
 
 func TestErrorAs(t *testing.T) {
-	mockT := new(testing.T)
 	tests := []struct {
 		err    error
 		result bool
@@ -3282,9 +3281,38 @@ func TestErrorAs(t *testing.T) {
 		tt := tt
 		var target *customError
 		t.Run(fmt.Sprintf("ErrorAs(%#v,%#v)", tt.err, target), func(t *testing.T) {
+			mockT := new(testing.T)
 			res := ErrorAs(mockT, tt.err, &target)
 			if res != tt.result {
-				t.Errorf("ErrorAs(%#v,%#v) should return %t)", tt.err, target, tt.result)
+				t.Errorf("ErrorAs(%#v,%#v) should return %t", tt.err, target, tt.result)
+			}
+			if res == mockT.Failed() {
+				t.Errorf("The test result (%t) should be reflected in the testing.T type (%t)", res, !mockT.Failed())
+			}
+		})
+	}
+}
+
+func TestNotErrorAs(t *testing.T) {
+	tests := []struct {
+		err    error
+		result bool
+	}{
+		{fmt.Errorf("wrap: %w", &customError{}), false},
+		{io.EOF, true},
+		{nil, true},
+	}
+	for _, tt := range tests {
+		tt := tt
+		var target *customError
+		t.Run(fmt.Sprintf("NotErrorAs(%#v,%#v)", tt.err, target), func(t *testing.T) {
+			mockT := new(testing.T)
+			res := NotErrorAs(mockT, tt.err, &target)
+			if res != tt.result {
+				t.Errorf("NotErrorAs(%#v,%#v) should not return %t", tt.err, target, tt.result)
+			}
+			if res == mockT.Failed() {
+				t.Errorf("The test result (%t) should be reflected in the testing.T type (%t)", res, !mockT.Failed())
 			}
 		})
 	}