add initial test

plugin/resolvergen/resolver_test.go

@@ -84,6 +84,24 @@ func TestOmitTemplateComment(t *testing.T) {
 	assertNoErrors(t, "github.com/99designs/gqlgen/plugin/resolvergen/testdata/omit_template_comment/out")
 }
 
+func TestResolver_Implementation(t *testing.T) {
+	_ = syscall.Unlink("testdata/resolver_implementor/resolver.go")
+
+	cfg, err := config.LoadConfig("testdata/resolver_implementor/gqlgen.yml")
+	require.NoError(t, err)
+	p := Plugin{}
+
+	require.NoError(t, cfg.Init())
+
+	data, err := codegen.BuildData(cfg, &implementorTest{})
+	if err != nil {
+		panic(err)
+	}
+
+	require.NoError(t, p.GenerateCode(data))
+	assertNoErrors(t, "github.com/99designs/gqlgen/plugin/resolvergen/testdata/resolver_implementor/out")
+}
+
 func TestCustomResolverTemplate(t *testing.T) {
 	_ = syscall.Unlink("testdata/resolvertemplate/out/resolver.go")
 	cfg, err := config.LoadConfig("testdata/resolvertemplate/gqlgen.yml")
@@ -142,3 +160,9 @@ func assertNoErrors(t *testing.T, pkg string) {
 		t.Fatal("see compilation errors above")
 	}
 }
+
+type implementorTest struct{}
+
+func (i *implementorTest) Implement(field *codegen.Field) string {
+	return "panic(\"implementor implemented me\")"
+}

plugin/resolvergen/testdata/resolver_implementor/gqlgen.yml

@@ -0,0 +1,15 @@
+schema:
+  - "testdata/schema.graphql"
+
+exec:
+  filename: testdata/resolver_implementor/out/ignored.go
+model:
+  filename: testdata/resolver_implementor/out/generated.go
+resolver:
+  type: CustomResolverType
+  layout: follow-schema
+  dir: testdata/resolver_implementor/out
+
+models:
+  Resolver:
+    model: github.com/99designs/gqlgen/plugin/resolvergen/testdata/resolver_implementor/out.Resolver

plugin/resolvergen/testdata/resolver_implementor/out/model.go

@@ -0,0 +1,13 @@
+package customresolver
+
+import "context"
+
+type Resolver struct{}
+
+type QueryResolver interface {
+	Resolver(ctx context.Context) (*Resolver, error)
+}
+
+type ResolverResolver interface {
+	Name(ctx context.Context, obj *Resolver) (string, error)
+}

plugin/resolvergen/testdata/resolver_implementor/out/resolver.go

@@ -0,0 +1,7 @@
+package customresolver
+
+// This file will not be regenerated automatically.
+//
+// It serves as dependency injection for your app, add any dependencies you require here.
+
+type CustomResolverType struct{}