diff --git a/staticlibs/native/tcutils/Android.bp b/staticlibs/native/tcutils/Android.bp
index c26fca6..e819e4c 100644
--- a/staticlibs/native/tcutils/Android.bp
+++ b/staticlibs/native/tcutils/Android.bp
@@ -42,3 +42,27 @@
         "//system/netd/server",
     ],
 }
+
+cc_test {
+    name: "libtcutils_test",
+    srcs: [
+        "tests/tcutils_test.cpp",
+    ],
+    cflags: [
+        "-Wall",
+        "-Werror",
+        "-Wno-error=unused-variable",
+    ],
+    header_libs: ["bpf_syscall_wrappers"],
+    static_libs: [
+        "libgmock",
+        "libtcutils",
+    ],
+    shared_libs: [
+        "libbase",
+        "liblog",
+    ],
+    min_sdk_version: "30",
+    require_root: true,
+    test_suites: ["general-tests"],
+}
diff --git a/staticlibs/native/tcutils/tcutils.cpp b/staticlibs/native/tcutils/tcutils.cpp
index 00f3c56..3f24178 100644
--- a/staticlibs/native/tcutils/tcutils.cpp
+++ b/staticlibs/native/tcutils/tcutils.cpp
@@ -175,7 +175,7 @@
   if (rv < 0) {
     logError("Get hardware address type of interface %s failed: %s", iface,
              strerror(-rv));
-    return -rv;
+    return rv;
   }
 
   // Backwards compatibility with pre-GKI kernels that use various custom
@@ -208,7 +208,7 @@
     return 0;
   default:
     logError("Unknown hardware address type %d on interface %s", rv, iface);
-    return -ENOENT;
+    return -EAFNOSUPPORT;
   }
 }
 
diff --git a/staticlibs/native/tcutils/tests/tcutils_test.cpp b/staticlibs/native/tcutils/tests/tcutils_test.cpp
new file mode 100644
index 0000000..bab2d3e
--- /dev/null
+++ b/staticlibs/native/tcutils/tests/tcutils_test.cpp
@@ -0,0 +1,66 @@
+/*
+ * Copyright 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * TcUtilsTest.cpp - unit tests for TcUtils.cpp
+ */
+
+#include <gtest/gtest.h>
+
+#include <tcutils/tcutils.h>
+
+#include <errno.h>
+
+namespace android {
+
+TEST(LibTcUtilsTest, IsEthernetOfNonExistingIf) {
+  bool result = false;
+  int error = isEthernet("not_existing_if", result);
+  ASSERT_FALSE(result);
+  ASSERT_EQ(-ENODEV, error);
+}
+
+TEST(LibTcUtilsTest, IsEthernetOfLoopback) {
+  bool result = false;
+  int error = isEthernet("lo", result);
+  ASSERT_FALSE(result);
+  ASSERT_EQ(-EAFNOSUPPORT, error);
+}
+
+// If wireless 'wlan0' interface exists it should be Ethernet.
+// See also HardwareAddressTypeOfWireless.
+TEST(LibTcUtilsTest, IsEthernetOfWireless) {
+  bool result = false;
+  int error = isEthernet("wlan0", result);
+  if (!result && error == -ENODEV)
+    return;
+
+  ASSERT_EQ(0, error);
+  ASSERT_TRUE(result);
+}
+
+// If cellular 'rmnet_data0' interface exists it should
+// *probably* not be Ethernet and instead be RawIp.
+// See also HardwareAddressTypeOfCellular.
+TEST(LibTcUtilsTest, IsEthernetOfCellular) {
+  bool result = false;
+  int error = isEthernet("rmnet_data0", result);
+  if (!result && error == -ENODEV)
+    return;
+
+  ASSERT_EQ(0, error);
+  ASSERT_FALSE(result);
+}
+
+} // namespace android