add test

sdk/test/trace/BUILD

@@ -41,3 +41,14 @@ cc_test(
         "@com_google_googletest//:gtest_main",
     ],
 )
+
+cc_test(
+    name = "always_on_sampler_test",
+    srcs = [
+        "always_on_sampler_test.cc",
+    ],
+    deps = [
+        "//sdk/src/trace",
+        "@com_google_googletest//:gtest_main",
+    ],
+)

sdk/test/trace/always_on_sampler_test.cc

@@ -0,0 +1,37 @@
+#include "opentelemetry/sdk/trace/always_on_sampler.h"
+#include "opentelemetry/nostd/span.h"
+
+#include <gtest/gtest.h>
+
+using namespace opentelemetry::sdk::trace;
+using namespace opentelemetry::nostd;
+
+TEST(AlwaysOnSampler, ShouldSample)
+{
+  AlwaysOnSampler sampler;
+
+  // A buffer of trace_id with no specific meaning
+  constexpr uint8_t buf[] = {0, 1, 2, 3, 4, 5, 6, 7, 0, 1, 2, 3, 4, 5, 6, 7};
+
+  trace_api::TraceId trace_id_invalid;
+  trace_api::TraceId trace_id_valid(buf);
+
+  auto sampling_result = sampler.ShouldSample(nullptr, trace_id_invalid, "invalid trace id test",
+                                              trace_api::SpanKind::kServer, span<AttributeKeyValue>());
+
+  ASSERT_EQ(Decision::RECORD_AND_SAMPLE, sampling_result.decision);
+  ASSERT_EQ(0, sampling_result.attributes->size());
+
+  sampling_result = sampler.ShouldSample(nullptr, trace_id_valid, "valid trace id test",
+                                              trace_api::SpanKind::kServer, span<AttributeKeyValue>());
+
+  ASSERT_EQ(Decision::RECORD_AND_SAMPLE, sampling_result.decision);
+  ASSERT_EQ(0, sampling_result.attributes->size());
+}
+
+TEST(AlwaysOnSampler, GetDescription)
+{
+  AlwaysOnSampler sampler;
+
+  ASSERT_EQ("AlwaysOnSampler", sampler.GetDescription());
+}