Add test with explicit and implicit importpath

tests/core/go_proto_library_importpath/BUILD.bazel

@@ -0,0 +1,36 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
+load("@io_bazel_rules_go//proto:def.bzl", "go_proto_library")
+load("@rules_proto//proto:defs.bzl", "proto_library")
+
+# Common rules
+proto_library(
+    name = "foo_proto",
+    srcs = ["foo.proto"],
+)
+
+go_proto_library(
+    name = "foo_go_proto",
+    importpath = "path/to/foo_go",
+    proto = ":foo_proto",
+)
+
+proto_library(
+    name = "bar_proto",
+    srcs = ["bar.proto"],
+    deps = [":foo_proto"],
+)
+
+go_proto_library(
+    name = "bar_go_proto",
+    proto = ":bar_proto",
+    deps = [":foo_go_proto"],
+)
+
+go_test(
+    name = "importpath_test",
+    srcs = ["importpath_test.go"],
+    deps = [
+        ":bar_go_proto",
+        ":foo_go_proto",
+    ],
+)

tests/core/go_proto_library_importpath/bar.proto

@@ -0,0 +1,9 @@
+syntax = "proto3";
+
+package tests.core.go_proto_library_importpath.bar;
+
+import "tests/core/go_proto_library_importpath/foo.proto";
+
+message Bar {
+  foo.Foo value = 1;
+}

tests/core/go_proto_library_importpath/foo.proto

@@ -0,0 +1,7 @@
+syntax = "proto3";
+
+package tests.core.go_proto_library_importpath.foo;
+
+message Foo {
+  int64 value = 1;
+}

tests/core/go_proto_library_importpath/importpath_test.go

@@ -0,0 +1,22 @@
+package importpath_test
+
+import (
+	"fmt"
+	"testing"
+
+	bar_proto "tests/core/go_proto_library_importpath/bar_go_proto"
+	foo_proto "path/to/foo_go"
+)
+
+func Test(t *testing.T) {
+	bar := &bar_proto.Bar{}
+	bar.Value = &foo_proto.Foo{}
+	bar.Value.Value = 5
+
+	var expected int64 = 5
+	if bar.Value.Value != expected {
+		t.Errorf(fmt.Sprintf("Not equal: \n"+
+			"expected: %s\n"+
+			"actual  : %s", expected, bar.Value.Value))
+	}
+}