tracing: add tests for otlp exporter and env vars

Add unit tests in pkg/tracing/plugin/otlp_test.go to verify newExporter,
checkDisabled, and newTracer with the OpenTelemetry environment
variables that replaced the deprecated OTLP plugin configuration fields.

Assisted-by: Antigravity
Signed-off-by: Samuel Karp <samuelkarp@google.com>

pkg/tracing/plugin/otlp_test.go

@@ -0,0 +1,163 @@
+/*
+   Copyright The containerd Authors.
+
+   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.
+*/
+
+package plugin
+
+import (
+	"context"
+	"errors"
+	"testing"
+
+	"github.com/containerd/errdefs"
+	"github.com/containerd/plugin"
+	"go.opentelemetry.io/otel/sdk/trace"
+	"go.opentelemetry.io/otel/sdk/trace/tracetest"
+)
+
+func TestNewExporter(t *testing.T) {
+	for _, tc := range []struct {
+		name           string
+		protocol       string
+		tracesProtocol string
+		output         error
+	}{
+		{
+			name:     "Test http/protobuf protocol, expect no error",
+			protocol: "http/protobuf",
+			output:   nil,
+		},
+		{
+			name:     "Test default protocol, expect no error",
+			protocol: "",
+			output:   nil,
+		},
+		{
+			name:     "Test grpc protocol, expect no error",
+			protocol: "grpc",
+			output:   nil,
+		},
+		{
+			name:     "Test http/json protocol which is not supported, expect not implemented error",
+			protocol: "http/json",
+			output:   errdefs.ErrNotImplemented,
+		},
+		{
+			name:           "Test traces protocol takes precedence over protocol",
+			protocol:       "http/json",
+			tracesProtocol: "http/protobuf",
+			output:         nil,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Setenv(otlpProtocolEnv, tc.protocol)
+			t.Setenv(otlpTracesProtocolEnv, tc.tracesProtocol)
+
+			ctx := context.TODO()
+			exp, err := newExporter(ctx)
+			if tc.output == nil {
+				if err != nil {
+					t.Fatalf("unexpected error: %v", err)
+				}
+				if exp == nil {
+					t.Fatal("expected exporter to be created, got nil")
+				}
+			} else {
+				if !errors.Is(err, tc.output) {
+					t.Fatalf("expected error %v, got %v", tc.output, err)
+				}
+			}
+		})
+	}
+}
+
+func TestCheckDisabled(t *testing.T) {
+	for _, tc := range []struct {
+		name           string
+		endpoint       string
+		tracesEndpoint string
+		sdkDisabled    string
+		output         error
+	}{
+		{
+			name:   "No endpoint configured, expect ErrSkipPlugin",
+			output: plugin.ErrSkipPlugin,
+		},
+		{
+			name:     "OTEL_EXPORTER_OTLP_ENDPOINT configured, expect no error",
+			endpoint: "http://localhost:4318",
+			output:   nil,
+		},
+		{
+			name:           "OTEL_EXPORTER_OTLP_TRACES_ENDPOINT configured, expect no error",
+			tracesEndpoint: "http://localhost:4318",
+			output:         nil,
+		},
+		{
+			name:        "OTEL_SDK_DISABLED=true with endpoint, expect ErrSkipPlugin",
+			endpoint:    "http://localhost:4318",
+			sdkDisabled: "true",
+			output:      plugin.ErrSkipPlugin,
+		},
+		{
+			name:        "OTEL_SDK_DISABLED=1 with endpoint, expect ErrSkipPlugin",
+			endpoint:    "http://localhost:4318",
+			sdkDisabled: "1",
+			output:      plugin.ErrSkipPlugin,
+		},
+		{
+			name:        "OTEL_SDK_DISABLED=false with endpoint, expect no error",
+			endpoint:    "http://localhost:4318",
+			sdkDisabled: "false",
+			output:      nil,
+		},
+		{
+			name:        "OTEL_SDK_DISABLED invalid value, expect ErrInvalidArgument",
+			endpoint:    "http://localhost:4318",
+			sdkDisabled: "invalid",
+			output:      errdefs.ErrInvalidArgument,
+		},
+	} {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Setenv(otlpEndpointEnv, tc.endpoint)
+			t.Setenv(otlpTracesEndpointEnv, tc.tracesEndpoint)
+			t.Setenv(sdkDisabledEnv, tc.sdkDisabled)
+
+			err := checkDisabled()
+			if tc.output == nil {
+				if err != nil {
+					t.Fatalf("unexpected error: %v", err)
+				}
+			} else {
+				if !errors.Is(err, tc.output) {
+					t.Fatalf("expected error %v, got %v", tc.output, err)
+				}
+			}
+		})
+	}
+}
+
+func TestNewTracer(t *testing.T) {
+	exp := tracetest.NewInMemoryExporter()
+	proc := trace.NewBatchSpanProcessor(exp)
+	procs := []trace.SpanProcessor{proc}
+
+	ctx := context.TODO()
+	tracerCloser, err := newTracer(ctx, procs)
+	if err != nil {
+		t.Fatalf("unexpected error creating tracer: %v", err)
+	}
+	defer tracerCloser.Close()
+}