test(view): improve test coverage (#7543)

Cover edge cases in config parser. Add rudimentary View/Filter
tests. Improves test coverage from 44% to 82%.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

plugin/view/view_test.go

@@ -0,0 +1,71 @@
+package view
+
+import (
+	"context"
+	"testing"
+
+	"github.com/coredns/coredns/plugin/pkg/expression"
+	ptest "github.com/coredns/coredns/plugin/test"
+	"github.com/coredns/coredns/request"
+
+	"github.com/expr-lang/expr"
+	"github.com/expr-lang/expr/vm"
+	"github.com/miekg/dns"
+)
+
+func TestFilter_NoPrograms(t *testing.T) {
+	v := &View{viewName: "test"}
+	st := makeState(t, "example.com.")
+	if !v.Filter(context.Background(), st) {
+		t.Fatalf("expected true when no programs are configured")
+	}
+}
+
+func TestFilter_ErrorPaths(t *testing.T) {
+	st := makeState(t, "example.com.")
+
+	tests := []struct {
+		expr     string
+		expected bool
+	}{
+		{"name() == 'example.com.'", true},
+		{"name() == 'notexample.com.'", false},
+		{"1", false},
+		{"incidr('invalid', '1.2.3.0/24')", false},
+	}
+
+	for i, tc := range tests {
+		v := &View{progs: []*vm.Program{compileExpr(t, tc.expr)}}
+		got := v.Filter(context.Background(), st)
+		if got != tc.expected {
+			t.Fatalf("case %d expr %q: expected %v, got %v", i, tc.expr, tc.expected, got)
+		}
+	}
+}
+
+func TestView_Names(t *testing.T) {
+	v := &View{viewName: "v1"}
+	if v.ViewName() != "v1" {
+		t.Fatalf("ViewName() expected %q, got %q", "v1", v.ViewName())
+	}
+	if v.Name() != "view" {
+		t.Fatalf("Name() expected %q, got %q", "view", v.Name())
+	}
+}
+
+func compileExpr(t *testing.T, e string) *vm.Program {
+	t.Helper()
+	prog, err := expr.Compile(e, expr.Env(expression.DefaultEnv(context.Background(), nil)), expr.DisableBuiltin("type"))
+	if err != nil {
+		t.Fatalf("compile failed for %q: %v", e, err)
+	}
+	return prog
+}
+
+func makeState(t *testing.T, qname string) *request.Request {
+	t.Helper()
+	m := new(dns.Msg)
+	m.SetQuestion(dns.Fqdn(qname), dns.TypeA)
+	w := &ptest.ResponseWriter{}
+	return &request.Request{W: w, Req: m}
+}