Create a export.Checkpointer API; refactor metric export pipeline test helpers (#1055)

* Add regexp filter in api/label, test

* Add regexp option to sdk.Config

* Return indistinct values only when keyRe != nil

* Filter in sdk

* Add an accumulator filter test

* SDK tests pass

* Precommit

* Undo set filters

* Backout related filter changes

* Add a new test

* Checkpoint

* Comments

* Comments in label.Set

* Lint

* Add Checkpointer

* Test refactor continues

* Refactor reducer test

* Checkpoint

* Update push_test

* Update pull controller

* Comment

* Remove pending PRs

* Remove exportertest pkg

* Revert basic changes

* Revert testing changes

* Restore processortest changes

* Precommit & comments

* Comments on pull semantics

* Comments

* Fix buggy test; incorrect expectation following error

* Finish this test

* Comments

* Apply suggestions from code review

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

Co-authored-by: Tyler Yahn <MrAlias@users.noreply.github.com>

example/otel-collector/main.go

@@ -31,6 +31,7 @@ import (
 	apitrace "go.opentelemetry.io/otel/api/trace"
 	"go.opentelemetry.io/otel/exporters/otlp"
 	"go.opentelemetry.io/otel/sdk/metric/controller/push"
+	"go.opentelemetry.io/otel/sdk/metric/processor/basic"
 	"go.opentelemetry.io/otel/sdk/metric/selector/simple"
 	"go.opentelemetry.io/otel/sdk/resource"
 	sdktrace "go.opentelemetry.io/otel/sdk/trace"
@@ -64,8 +65,11 @@ func initProvider() (*otlp.Exporter, *push.Controller) {
 	handleErr(err, "failed to create trace provider")
 
 	pusher := push.New(
+		basic.New(
 			simple.NewWithExactDistribution(),
 			exp,
+		),
+		exp,
 		push.WithPeriod(2*time.Second),
 	)
 

exporters/metric/prometheus/prometheus.go

@@ -29,6 +29,7 @@ import (
 	export "go.opentelemetry.io/otel/sdk/export/metric"
 	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
 	"go.opentelemetry.io/otel/sdk/metric/controller/pull"
+	"go.opentelemetry.io/otel/sdk/metric/processor/basic"
 	"go.opentelemetry.io/otel/sdk/metric/selector/simple"
 )
 
@@ -144,8 +145,11 @@ func (e *Exporter) SetController(config Config, options ...pull.Option) {
 	defer e.lock.Unlock()
 
 	e.controller = pull.New(
+		basic.New(
 			simple.NewWithHistogramDistribution(config.DefaultHistogramBoundaries),
 			e,
+			basic.WithMemory(true),
+		),
 		options...,
 	)
 }

exporters/stdout/exporter.go

@@ -20,6 +20,7 @@ import (
 	"go.opentelemetry.io/otel/sdk/export/metric"
 	"go.opentelemetry.io/otel/sdk/export/trace"
 	"go.opentelemetry.io/otel/sdk/metric/controller/push"
+	"go.opentelemetry.io/otel/sdk/metric/processor/basic"
 	"go.opentelemetry.io/otel/sdk/metric/selector/simple"
 	sdktrace "go.opentelemetry.io/otel/sdk/trace"
 )
@@ -62,8 +63,11 @@ func NewExportPipeline(exportOpts []Option, pushOpts []push.Option) (apitrace.Pr
 	}
 
 	pusher := push.New(
+		basic.New(
 			simple.NewWithExactDistribution(),
 			exporter,
+		),
+		exporter,
 		pushOpts...,
 	)
 	pusher.Start()

sdk/export/metric/metric.go

@@ -97,6 +97,33 @@ type AggregatorSelector interface {
 	AggregatorFor(*metric.Descriptor, ...*Aggregator)
 }
 
+// Checkpointer is the interface used by a Controller to coordinate
+// the Processor with Accumulator(s) and Exporter(s).  The
+// StartCollection() and FinishCollection() methods start and finish a
+// collection interval.  Controllers call the Accumulator(s) during
+// collection to process Accumulations.
+type Checkpointer interface {
+	// Processor processes metric data for export.  The Process
+	// method is bracketed by StartCollection and FinishCollection
+	// calls.  The embedded AggregatorSelector can be called at
+	// any time.
+	Processor
+
+	// CheckpointSet returns the current data set.  This may be
+	// called before and after collection.  The
+	// implementation is required to return the same value
+	// throughout its lifetime, since CheckpointSet exposes a
+	// sync.Locker interface.  The caller is responsible for
+	// locking the CheckpointSet before initiating collection.
+	CheckpointSet() CheckpointSet
+
+	// StartCollection begins a collection interval.
+	StartCollection()
+
+	// FinishCollection ends a collection interval.
+	FinishCollection() error
+}
+
 // Aggregator implements a specific aggregation behavior, e.g., a
 // behavior to track a sequence of updates to an instrument.  Sum-only
 // instruments commonly use a simple Sum aggregator, but for the

sdk/export/metric/metrictest/test.go

@@ -35,6 +35,7 @@ type mapkey struct {
 }
 
 // CheckpointSet is useful for testing Exporters.
+// TODO(#872): Uses of this can be replaced by processortest.Output.
 type CheckpointSet struct {
 	sync.RWMutex
 	records  map[mapkey]export.Record

sdk/metric/controller/pull/pull.go

@@ -23,7 +23,6 @@ import (
 	export "go.opentelemetry.io/otel/sdk/export/metric"
 	sdk "go.opentelemetry.io/otel/sdk/metric"
 	controllerTime "go.opentelemetry.io/otel/sdk/metric/controller/time"
-	processor "go.opentelemetry.io/otel/sdk/metric/processor/basic"
 	"go.opentelemetry.io/otel/sdk/resource"
 )
 
@@ -36,7 +35,7 @@ const DefaultCachePeriod time.Duration = 10 * time.Second
 // Foreach() for accessing current records.
 type Controller struct {
 	accumulator  *sdk.Accumulator
-	processor   *processor.Processor
+	checkpointer export.Checkpointer
 	provider     *registry.Provider
 	period       time.Duration
 	lastCollect  time.Time
@@ -44,8 +43,14 @@ type Controller struct {
 	checkpoint   export.CheckpointSet
 }
 
-// New returns a *Controller configured with an aggregation selector and options.
+// New returns a *Controller configured with an export.Checkpointer.
-func New(aselector export.AggregatorSelector, eselector export.ExportKindSelector, options ...Option) *Controller {
+//
+// Pull controllers are typically used in an environment where there
+// are multiple readers.  It is common, therefore, when configuring a
+// basic Processor for use with this controller, to use a
+// CumulativeExport strategy and the basic.WithMemory(true) option,
+// which ensures that every CheckpointSet includes full state.
+func New(checkpointer export.Checkpointer, options ...Option) *Controller {
 	config := &Config{
 		Resource:    resource.Empty(),
 		CachePeriod: DefaultCachePeriod,
@@ -53,27 +58,24 @@ func New(aselector export.AggregatorSelector, eselector export.ExportKindSelecto
 	for _, opt := range options {
 		opt.Apply(config)
 	}
-	// This controller uses WithMemory() as a requirement to
-	// support multiple readers.
-	processor := processor.New(aselector, eselector, processor.WithMemory(true))
 	accum := sdk.NewAccumulator(
-		processor,
+		checkpointer,
 		sdk.WithResource(config.Resource),
 	)
 	return &Controller{
 		accumulator:  accum,
-		processor:   processor,
+		checkpointer: checkpointer,
 		provider:     registry.NewProvider(accum),
 		period:       config.CachePeriod,
-		checkpoint:  processor.CheckpointSet(),
+		checkpoint:   checkpointer.CheckpointSet(),
 		clock:        controllerTime.RealClock{},
 	}
 }
 
 // SetClock sets the clock used for caching.  For testing purposes.
 func (c *Controller) SetClock(clock controllerTime.Clock) {
-	c.processor.Lock()
+	c.checkpointer.CheckpointSet().Lock()
-	defer c.processor.Unlock()
+	defer c.checkpointer.CheckpointSet().Unlock()
 	c.clock = clock
 }
 
@@ -86,8 +88,8 @@ func (c *Controller) Provider() metric.Provider {
 // Foreach gives the caller read-locked access to the current
 // export.CheckpointSet.
 func (c *Controller) ForEach(ks export.ExportKindSelector, f func(export.Record) error) error {
-	c.processor.RLock()
+	c.checkpointer.CheckpointSet().RLock()
-	defer c.processor.RUnlock()
+	defer c.checkpointer.CheckpointSet().RUnlock()
 
 	return c.checkpoint.ForEach(ks, f)
 }
@@ -95,8 +97,8 @@ func (c *Controller) ForEach(ks export.ExportKindSelector, f func(export.Record)
 // Collect requests a collection.  The collection will be skipped if
 // the last collection is aged less than the CachePeriod.
 func (c *Controller) Collect(ctx context.Context) error {
-	c.processor.Lock()
+	c.checkpointer.CheckpointSet().Lock()
-	defer c.processor.Unlock()
+	defer c.checkpointer.CheckpointSet().Unlock()
 
 	if c.period > 0 {
 		now := c.clock.Now()
@@ -108,9 +110,9 @@ func (c *Controller) Collect(ctx context.Context) error {
 		c.lastCollect = now
 	}
 
-	c.processor.StartCollection()
+	c.checkpointer.StartCollection()
 	c.accumulator.Collect(ctx)
-	err := c.processor.FinishCollection()
+	err := c.checkpointer.FinishCollection()
-	c.checkpoint = c.processor.CheckpointSet()
+	c.checkpoint = c.checkpointer.CheckpointSet()
 	return err
 }

sdk/metric/controller/pull/pull_test.go

@@ -28,14 +28,18 @@ import (
 	export "go.opentelemetry.io/otel/sdk/export/metric"
 	"go.opentelemetry.io/otel/sdk/metric/controller/controllertest"
 	"go.opentelemetry.io/otel/sdk/metric/controller/pull"
+	"go.opentelemetry.io/otel/sdk/metric/processor/basic"
 	"go.opentelemetry.io/otel/sdk/metric/processor/processortest"
 	selector "go.opentelemetry.io/otel/sdk/metric/selector/simple"
 )
 
 func TestPullNoCache(t *testing.T) {
 	puller := pull.New(
+		basic.New(
 			selector.NewWithExactDistribution(),
 			export.CumulativeExporter,
+			basic.WithMemory(true),
+		),
 		pull.WithCachePeriod(0),
 	)
 
@@ -66,8 +70,11 @@ func TestPullNoCache(t *testing.T) {
 
 func TestPullWithCache(t *testing.T) {
 	puller := pull.New(
+		basic.New(
 			selector.NewWithExactDistribution(),
 			export.CumulativeExporter,
+			basic.WithMemory(true),
+		),
 		pull.WithCachePeriod(time.Second),
 	)
 	mock := controllertest.NewMockClock()

sdk/metric/controller/push/push.go

@@ -25,7 +25,6 @@ import (
 	export "go.opentelemetry.io/otel/sdk/export/metric"
 	sdk "go.opentelemetry.io/otel/sdk/metric"
 	controllerTime "go.opentelemetry.io/otel/sdk/metric/controller/time"
-	"go.opentelemetry.io/otel/sdk/metric/processor/basic"
 )
 
 // DefaultPushPeriod is the default time interval between pushes.
@@ -36,7 +35,7 @@ type Controller struct {
 	lock         sync.Mutex
 	accumulator  *sdk.Accumulator
 	provider     *registry.Provider
-	processor   *basic.Processor
+	checkpointer export.Checkpointer
 	exporter     export.Exporter
 	wg           sync.WaitGroup
 	ch           chan struct{}
@@ -47,9 +46,9 @@ type Controller struct {
 }
 
 // New constructs a Controller, an implementation of metric.Provider,
-// using the provided exporter and options to configure an SDK with
+// using the provided checkpointer, exporter, and options to configure
-// periodic collection.
+// an SDK with periodic collection.
-func New(selector export.AggregatorSelector, exporter export.Exporter, opts ...Option) *Controller {
+func New(checkpointer export.Checkpointer, exporter export.Exporter, opts ...Option) *Controller {
 	c := &Config{
 		Period: DefaultPushPeriod,
 	}
@@ -60,15 +59,14 @@ func New(selector export.AggregatorSelector, exporter export.Exporter, opts ...O
 		c.Timeout = c.Period
 	}
 
-	processor := basic.New(selector, exporter)
 	impl := sdk.NewAccumulator(
-		processor,
+		checkpointer,
 		sdk.WithResource(c.Resource),
 	)
 	return &Controller{
 		provider:     registry.NewProvider(impl),
 		accumulator:  impl,
-		processor:   processor,
+		checkpointer: checkpointer,
 		exporter:     exporter,
 		ch:           make(chan struct{}),
 		period:       c.Period,
@@ -139,16 +137,17 @@ func (c *Controller) tick() {
 	ctx, cancel := context.WithTimeout(context.Background(), c.timeout)
 	defer cancel()
 
-	c.processor.Lock()
+	ckpt := c.checkpointer.CheckpointSet()
-	defer c.processor.Unlock()
+	ckpt.Lock()
+	defer ckpt.Unlock()
 
-	c.processor.StartCollection()
+	c.checkpointer.StartCollection()
 	c.accumulator.Collect(ctx)
-	if err := c.processor.FinishCollection(); err != nil {
+	if err := c.checkpointer.FinishCollection(); err != nil {
 		global.Handle(err)
 	}
 
-	if err := c.exporter.Export(ctx, c.processor.CheckpointSet()); err != nil {
+	if err := c.exporter.Export(ctx, ckpt); err != nil {
 		global.Handle(err)
 	}
 }

sdk/metric/controller/push/push_test.go

@@ -30,10 +30,10 @@ import (
 	"go.opentelemetry.io/otel/api/metric"
 	export "go.opentelemetry.io/otel/sdk/export/metric"
 	"go.opentelemetry.io/otel/sdk/export/metric/aggregation"
-	"go.opentelemetry.io/otel/sdk/export/metric/metrictest"
 	"go.opentelemetry.io/otel/sdk/metric/controller/controllertest"
 	"go.opentelemetry.io/otel/sdk/metric/controller/push"
-	"go.opentelemetry.io/otel/sdk/metric/processor/processortest"
+	"go.opentelemetry.io/otel/sdk/metric/processor/basic"
+	processorTest "go.opentelemetry.io/otel/sdk/metric/processor/processortest"
 	"go.opentelemetry.io/otel/sdk/resource"
 )
 
@@ -65,85 +65,46 @@ func init() {
 	global.SetErrorHandler(testHandler)
 }
 
-type testExporter struct {
+func newExporter() *processorTest.Exporter {
-	t         *testing.T
+	return processorTest.NewExporter(
-	lock      sync.Mutex
+		export.PassThroughExporter,
-	exports   int
+		label.DefaultEncoder(),
-	records   []export.Record
+	)
-	injectErr func(r export.Record) error
 }
 
-type testFixture struct {
+func newCheckpointer() export.Checkpointer {
-	checkpointSet *metrictest.CheckpointSet
+	return processorTest.Checkpointer(
-	exporter      *testExporter
+		processorTest.NewProcessor(
-}
+			processorTest.AggregatorSelector(),
-
+			label.DefaultEncoder(),
-func newFixture(t *testing.T) testFixture {
+		),
-	checkpointSet := metrictest.NewCheckpointSet(testResource)
+	)
-
-	exporter := &testExporter{
-		t: t,
-	}
-	return testFixture{
-		checkpointSet: checkpointSet,
-		exporter:      exporter,
-	}
-}
-
-func (e *testExporter) ExportKindFor(*metric.Descriptor, aggregation.Kind) export.ExportKind {
-	return export.PassThroughExporter
-}
-
-func (e *testExporter) Export(_ context.Context, checkpointSet export.CheckpointSet) error {
-	e.lock.Lock()
-	defer e.lock.Unlock()
-	e.exports++
-	var records []export.Record
-	if err := checkpointSet.ForEach(e, func(r export.Record) error {
-		if e.injectErr != nil {
-			if err := e.injectErr(r); err != nil {
-				return err
-			}
-		}
-		records = append(records, r)
-		return nil
-	}); err != nil {
-		return err
-	}
-	e.records = records
-	return nil
-}
-
-func (e *testExporter) resetRecords() ([]export.Record, int) {
-	e.lock.Lock()
-	defer e.lock.Unlock()
-	r := e.records
-	e.records = nil
-	return r, e.exports
 }
 
 func TestPushDoubleStop(t *testing.T) {
-	fix := newFixture(t)
+	exporter := newExporter()
-	p := push.New(processortest.AggregatorSelector(), fix.exporter)
+	checkpointer := newCheckpointer()
+	p := push.New(checkpointer, exporter)
 	p.Start()
 	p.Stop()
 	p.Stop()
 }
 
 func TestPushDoubleStart(t *testing.T) {
-	fix := newFixture(t)
+	exporter := newExporter()
-	p := push.New(processortest.AggregatorSelector(), fix.exporter)
+	checkpointer := newCheckpointer()
+	p := push.New(checkpointer, exporter)
 	p.Start()
 	p.Start()
 	p.Stop()
 }
 
 func TestPushTicker(t *testing.T) {
-	fix := newFixture(t)
+	exporter := newExporter()
-
+	checkpointer := newCheckpointer()
 	p := push.New(
-		processortest.AggregatorSelector(),
+		checkpointer,
-		fix.exporter,
+		exporter,
 		push.WithPeriod(time.Second),
 		push.WithResource(testResource),
 	)
@@ -160,39 +121,29 @@ func TestPushTicker(t *testing.T) {
 
 	counter.Add(ctx, 3)
 
-	records, exports := fix.exporter.resetRecords()
+	require.EqualValues(t, map[string]float64{}, exporter.Values())
-	require.Equal(t, 0, exports)
-	require.Equal(t, 0, len(records))
 
 	mock.Add(time.Second)
 	runtime.Gosched()
 
-	records, exports = fix.exporter.resetRecords()
+	require.EqualValues(t, map[string]float64{
-	require.Equal(t, 1, exports)
+		"counter.sum//R=V": 3,
-	require.Equal(t, 1, len(records))
+	}, exporter.Values())
-	require.Equal(t, "counter.sum", records[0].Descriptor().Name())
-	require.Equal(t, "R=V", records[0].Resource().Encoded(label.DefaultEncoder()))
 
-	sum, err := records[0].Aggregation().(aggregation.Sum).Sum()
+	require.Equal(t, 1, exporter.ExportCount())
-	require.Equal(t, int64(3), sum.AsInt64())
+	exporter.Reset()
-	require.Nil(t, err)
-
-	fix.checkpointSet.Reset()
 
 	counter.Add(ctx, 7)
 
 	mock.Add(time.Second)
 	runtime.Gosched()
 
-	records, exports = fix.exporter.resetRecords()
+	require.EqualValues(t, map[string]float64{
-	require.Equal(t, 2, exports)
+		"counter.sum//R=V": 10,
-	require.Equal(t, 1, len(records))
+	}, exporter.Values())
-	require.Equal(t, "counter.sum", records[0].Descriptor().Name())
-	require.Equal(t, "R=V", records[0].Resource().Encoded(label.DefaultEncoder()))
 
-	sum, err = records[0].Aggregation().(aggregation.Sum).Sum()
+	require.Equal(t, 1, exporter.ExportCount())
-	require.Equal(t, int64(7), sum.AsInt64())
+	exporter.Reset()
-	require.Nil(t, err)
 
 	p.Stop()
 }
@@ -210,21 +161,30 @@ func TestPushExportError(t *testing.T) {
 	var tests = []struct {
 		name          string
 		injectedError error
-		expectedDescriptors []string
+		expected      map[string]float64
 		expectedError error
 	}{
-		{"errNone", nil, []string{"counter1.sum{R=V,X=Y}", "counter2.sum{R=V,}"}, nil},
+		{"errNone", nil, map[string]float64{
-		{"errNoData", aggregation.ErrNoData, []string{"counter2.sum{R=V,}"}, nil},
+			"counter1.sum/X=Y/R=V": 3,
-		{"errUnexpected", errAggregator, []string{}, errAggregator},
+			"counter2.sum//R=V":    5,
+		}, nil},
+		{"errNoData", aggregation.ErrNoData, map[string]float64{
+			"counter2.sum//R=V": 5,
+		}, nil},
+		{"errUnexpected", errAggregator, map[string]float64{}, errAggregator},
 	}
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
-			fix := newFixture(t)
+			exporter := newExporter()
-			fix.exporter.injectErr = injector("counter1.sum", tt.injectedError)
+			exporter.InjectErr = injector("counter1.sum", tt.injectedError)
 
+			// This test validates the error handling
+			// behavior of the basic Processor is honored
+			// by the push processor.
+			checkpointer := basic.New(processorTest.AggregatorSelector(), exporter)
 			p := push.New(
-				processortest.AggregatorSelector(),
+				checkpointer,
-				fix.exporter,
+				exporter,
 				push.WithPeriod(time.Second),
 				push.WithResource(testResource),
 			)
@@ -244,31 +204,21 @@ func TestPushExportError(t *testing.T) {
 			counter1.Add(ctx, 3, kv.String("X", "Y"))
 			counter2.Add(ctx, 5)
 
-			require.Equal(t, 0, fix.exporter.exports)
+			require.Equal(t, 0, exporter.ExportCount())
 			require.Nil(t, testHandler.Flush())
 
 			mock.Add(time.Second)
 			runtime.Gosched()
 
-			records, exports := fix.exporter.resetRecords()
+			require.Equal(t, 1, exporter.ExportCount())
-			require.Equal(t, 1, exports)
 			if tt.expectedError == nil {
+				require.EqualValues(t, tt.expected, exporter.Values())
 				require.NoError(t, testHandler.Flush())
 			} else {
 				err := testHandler.Flush()
 				require.Error(t, err)
 				require.Equal(t, tt.expectedError, err)
 			}
-			require.Equal(t, len(tt.expectedDescriptors), len(records))
-			for _, r := range records {
-				require.Contains(t, tt.expectedDescriptors,
-					fmt.Sprintf("%s{%s,%s}",
-						r.Descriptor().Name(),
-						r.Resource().Encoded(label.DefaultEncoder()),
-						r.Labels().Encoded(label.DefaultEncoder()),
-					),
-				)
-			}
 
 			p.Stop()
 		})

sdk/metric/correct_test.go

@@ -69,6 +69,9 @@ func init() {
 	global.SetErrorHandler(testHandler)
 }
 
+// correctnessProcessor could be replaced with processortest.Processor
+// with a non-default aggregator selector.  TODO(#872) use the
+// processortest code here.
 type correctnessProcessor struct {
 	t *testing.T
 	*testSelector

sdk/metric/processor/basic/basic.go

@@ -117,11 +117,12 @@ type (
 )
 
 var _ export.Processor = &Processor{}
+var _ export.Checkpointer = &Processor{}
 var _ export.CheckpointSet = &state{}
 var ErrInconsistentState = fmt.Errorf("inconsistent processor state")
 var ErrInvalidExporterKind = fmt.Errorf("invalid exporter kind")
 
-// New returns a basic Processor using the provided
+// New returns a basic Processor that is also a Checkpointer using the provided
 // AggregatorSelector to select Aggregators.  The ExportKindSelector
 // is consulted to determine the kind(s) of exporter that will consume
 // data, so that this Processor can prepare to compute Delta or

sdk/metric/processor/processortest/test.go

@@ -15,8 +15,10 @@
 package processortest
 
 import (
+	"context"
 	"fmt"
 	"strings"
+	"sync"
 	"time"
 
 	"go.opentelemetry.io/otel/api/label"
@@ -29,33 +31,128 @@ import (
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/lastvalue"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/minmaxsumcount"
 	"go.opentelemetry.io/otel/sdk/metric/aggregator/sum"
+	"go.opentelemetry.io/otel/sdk/resource"
 )
 
 type (
-	nameWithNumKind struct {
+	// mapKey is the unique key for a metric, consisting of its
-		name       string
+	// unique descriptor, distinct labels, and distinct resource
-		numberKind metric.NumberKind
+	// attributes.
+	mapKey struct {
+		desc     *metric.Descriptor
+		labels   label.Distinct
+		resource label.Distinct
 	}
 
-	// Output collects distinct metric/label set outputs.
+	// mapValue is value stored in a processor used to produce a
+	// CheckpointSet.
+	mapValue struct {
+		labels     *label.Set
+		resource   *resource.Resource
+		aggregator export.Aggregator
+	}
+
+	// Output implements export.CheckpointSet.
 	Output struct {
-		m            map[nameWithNumKind]export.Aggregator
+		m            map[mapKey]mapValue
 		labelEncoder label.Encoder
+		sync.RWMutex
 	}
 
 	// testAggregatorSelector returns aggregators consistent with
 	// the test variables below, needed for testing stateful
 	// processors, which clone Aggregators using AggregatorFor(desc).
 	testAggregatorSelector struct{}
+
+	// testCheckpointer is a export.Checkpointer.
+	testCheckpointer struct {
+		started  int
+		finished int
+		*Processor
+	}
+
+	// Processor is a testing implementation of export.Processor that
+	// assembles its results as a map[string]float64.
+	Processor struct {
+		export.AggregatorSelector
+		output *Output
+	}
+
+	// Exporter is a testing implementation of export.Exporter that
+	// assembles its results as a map[string]float64.
+	Exporter struct {
+		export.ExportKindSelector
+		output      *Output
+		exportCount int
+
+		// InjectErr supports returning conditional errors from
+		// the Export() routine.  This must be set before the
+		// Exporter is first used.
+		InjectErr func(export.Record) error
+	}
 )
 
-func NewOutput(labelEncoder label.Encoder) Output {
+// NewProcessor returns a new testing Processor implementation.
-	return Output{
+// Verify expected outputs using Values(), e.g.:
-		m:            make(map[nameWithNumKind]export.Aggregator),
+//
-		labelEncoder: labelEncoder,
+//     require.EqualValues(t, map[string]float64{
+//         "counter.sum/A=1,B=2/R=V": 100,
+//     }, processor.Values())
+//
+// Where in the example A=1,B=2 is the encoded labels and R=V is the
+// encoded resource value.
+func NewProcessor(selector export.AggregatorSelector, encoder label.Encoder) *Processor {
+	return &Processor{
+		AggregatorSelector: selector,
+		output:             NewOutput(encoder),
 	}
 }
 
+// Process implements export.Processor.
+func (p *Processor) Process(accum export.Accumulation) error {
+	return p.output.AddAccumulation(accum)
+}
+
+// Values returns the mapping from label set to point values for the
+// accumulations that were processed.  Point values are chosen as
+// either the Sum or the LastValue, whichever is implemented.  (All
+// the built-in Aggregators implement one of these interfaces.)
+func (p *Processor) Values() map[string]float64 {
+	return p.output.Map()
+}
+
+// Checkpointer returns a checkpointer that computes a single
+// interval.
+func Checkpointer(p *Processor) export.Checkpointer {
+	return &testCheckpointer{
+		Processor: p,
+	}
+}
+
+// StartCollection implements export.Checkpointer.
+func (c *testCheckpointer) StartCollection() {
+	if c.started != c.finished {
+		panic(fmt.Sprintf("collection was already started: %d != %d", c.started, c.finished))
+	}
+
+	c.started++
+}
+
+// FinishCollection implements export.Checkpointer.
+func (c *testCheckpointer) FinishCollection() error {
+	if c.started-1 != c.finished {
+		return fmt.Errorf("collection was not started: %d != %d", c.started, c.finished)
+	}
+
+	c.finished++
+	return nil
+}
+
+// CheckpointSet implements export.Checkpointer.
+func (c *testCheckpointer) CheckpointSet() export.CheckpointSet {
+	return c.Processor.output
+}
+
 // AggregatorSelector returns a policy that is consistent with the
 // test descriptors above.  I.e., it returns sum.New() for counter
 // instruments and lastvalue.New() for lastValue instruments.
@@ -63,6 +160,7 @@ func AggregatorSelector() export.AggregatorSelector {
 	return testAggregatorSelector{}
 }
 
+// AggregatorFor implements export.AggregatorSelector.
 func (testAggregatorSelector) AggregatorFor(desc *metric.Descriptor, aggPtrs ...*export.Aggregator) {
 
 	switch {
@@ -105,49 +203,98 @@ func (testAggregatorSelector) AggregatorFor(desc *metric.Descriptor, aggPtrs ...
 	}
 }
 
+// NewOutput is a helper for testing an expected set of Accumulations
+// (from an Accumulator) or an expected set of Records (from a
+// Processor).  If testing with an Accumulator, it may be simpler to
+// use the test Processor in this package.
+func NewOutput(labelEncoder label.Encoder) *Output {
+	return &Output{
+		m:            make(map[mapKey]mapValue),
+		labelEncoder: labelEncoder,
+	}
+}
+
+// ForEach implements export.CheckpointSet.
+func (o *Output) ForEach(_ export.ExportKindSelector, ff func(export.Record) error) error {
+	for key, value := range o.m {
+		if err := ff(export.NewRecord(
+			key.desc,
+			value.labels,
+			value.resource,
+			value.aggregator.Aggregation(),
+			time.Time{},
+			time.Time{},
+		)); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 // AddRecord adds a string representation of the exported metric data
 // to a map for use in testing.  The value taken from the record is
 // either the Sum() or the LastValue() of its Aggregation(), whichever
 // is defined.  Record timestamps are ignored.
-func (o Output) AddRecord(rec export.Record) error {
+func (o *Output) AddRecord(rec export.Record) error {
-	encoded := rec.Labels().Encoded(o.labelEncoder)
+	key := mapKey{
-	rencoded := rec.Resource().Encoded(o.labelEncoder)
+		desc:     rec.Descriptor(),
-	key := nameWithNumKind{
+		labels:   rec.Labels().Equivalent(),
-		name:       fmt.Sprint(rec.Descriptor().Name(), "/", encoded, "/", rencoded),
+		resource: rec.Resource().Equivalent(),
-		numberKind: rec.Descriptor().NumberKind(),
 	}
-
 	if _, ok := o.m[key]; !ok {
 		var agg export.Aggregator
 		testAggregatorSelector{}.AggregatorFor(rec.Descriptor(), &agg)
-		o.m[key] = agg
+		o.m[key] = mapValue{
+			aggregator: agg,
+			labels:     rec.Labels(),
+			resource:   rec.Resource(),
 		}
-	return o.m[key].Merge(rec.Aggregation().(export.Aggregator), rec.Descriptor())
+	}
+	return o.m[key].aggregator.Merge(rec.Aggregation().(export.Aggregator), rec.Descriptor())
 }
 
-func (o Output) Map() map[string]float64 {
+// Map returns the calculated values for test validation from a set of
+// Accumulations or a set of Records.  When mapping records or
+// accumulations into floating point values, the Sum() or LastValue()
+// is chosen, whichever is implemented by the underlying Aggregator.
+func (o *Output) Map() map[string]float64 {
 	r := make(map[string]float64)
-	for nnk, agg := range o.m {
+	err := o.ForEach(export.PassThroughExporter, func(record export.Record) error {
-		value := 0.0
+		for key, value := range o.m {
-		if s, ok := agg.(aggregation.Sum); ok {
+			encoded := value.labels.Encoded(o.labelEncoder)
+			rencoded := value.resource.Encoded(o.labelEncoder)
+			number := 0.0
+			if s, ok := value.aggregator.(aggregation.Sum); ok {
 				sum, _ := s.Sum()
-			value = sum.CoerceToFloat64(nnk.numberKind)
+				number = sum.CoerceToFloat64(key.desc.NumberKind())
-		} else if l, ok := agg.(aggregation.LastValue); ok {
+			} else if l, ok := value.aggregator.(aggregation.LastValue); ok {
 				last, _, _ := l.LastValue()
-			value = last.CoerceToFloat64(nnk.numberKind)
+				number = last.CoerceToFloat64(key.desc.NumberKind())
 			} else {
-			panic(fmt.Sprintf("Unhandled aggregator type: %T", agg))
+				panic(fmt.Sprintf("Unhandled aggregator type: %T", value.aggregator))
 			}
-		r[nnk.name] = value
+			name := fmt.Sprint(key.desc.Name(), "/", encoded, "/", rencoded)
+			r[name] = number
+		}
+		return nil
+	})
+	if err != nil {
+		panic(fmt.Sprint("Unexpected processor error: ", err))
 	}
 	return r
 }
 
+// Reset restores the Output to its initial state, with no accumulated
+// metric data.
+func (o *Output) Reset() {
+	o.m = map[mapKey]mapValue{}
+}
+
 // AddAccumulation adds a string representation of the exported metric
 // data to a map for use in testing.  The value taken from the
 // accumulation is either the Sum() or the LastValue() of its
 // Aggregator().Aggregation(), whichever is defined.
-func (o Output) AddAccumulation(acc export.Accumulation) error {
+func (o *Output) AddAccumulation(acc export.Accumulation) error {
 	return o.AddRecord(
 		export.NewRecord(
 			acc.Descriptor(),
@@ -159,3 +306,60 @@ func (o Output) AddAccumulation(acc export.Accumulation) error {
 		),
 	)
 }
+
+// NewExporter returns a new testing Exporter implementation.
+// Verify exporter outputs using Values(), e.g.,:
+//
+//     require.EqualValues(t, map[string]float64{
+//         "counter.sum/A=1,B=2/R=V": 100,
+//     }, exporter.Values())
+//
+// Where in the example A=1,B=2 is the encoded labels and R=V is the
+// encoded resource value.
+func NewExporter(selector export.ExportKindSelector, encoder label.Encoder) *Exporter {
+	return &Exporter{
+		ExportKindSelector: selector,
+		output:             NewOutput(encoder),
+	}
+}
+
+func (e *Exporter) Export(_ context.Context, ckpt export.CheckpointSet) error {
+	e.output.Lock()
+	defer e.output.Unlock()
+	e.exportCount++
+	return ckpt.ForEach(e.ExportKindSelector, func(r export.Record) error {
+		if e.InjectErr != nil {
+			if err := e.InjectErr(r); err != nil {
+				return err
+			}
+		}
+		return e.output.AddRecord(r)
+	})
+}
+
+// Values returns the mapping from label set to point values for the
+// accumulations that were processed.  Point values are chosen as
+// either the Sum or the LastValue, whichever is implemented.  (All
+// the built-in Aggregators implement one of these interfaces.)
+func (e *Exporter) Values() map[string]float64 {
+	e.output.Lock()
+	defer e.output.Unlock()
+	return e.output.Map()
+}
+
+// ExportCount returns the number of times Export() has been called
+// since the last Reset().
+func (e *Exporter) ExportCount() int {
+	e.output.Lock()
+	defer e.output.Unlock()
+	return e.exportCount
+}
+
+// Reset sets the exporter's output to the initial, empty state and
+// resets the export count to zero.
+func (e *Exporter) Reset() {
+	e.output.Lock()
+	defer e.output.Unlock()
+	e.output.Reset()
+	e.exportCount = 0
+}

sdk/metric/processor/processortest/test_test.go

@@ -0,0 +1,87 @@
+// Copyright The OpenTelemetry 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 processortest_test
+
+import (
+	"context"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+
+	"go.opentelemetry.io/otel/api/kv"
+	"go.opentelemetry.io/otel/api/label"
+	"go.opentelemetry.io/otel/api/metric"
+	export "go.opentelemetry.io/otel/sdk/export/metric"
+	metricsdk "go.opentelemetry.io/otel/sdk/metric"
+	processorTest "go.opentelemetry.io/otel/sdk/metric/processor/processortest"
+	"go.opentelemetry.io/otel/sdk/resource"
+)
+
+func generateTestData(proc export.Processor) {
+	ctx := context.Background()
+	accum := metricsdk.NewAccumulator(
+		proc,
+		metricsdk.WithResource(
+			resource.New(kv.String("R", "V")),
+		),
+	)
+	meter := metric.WrapMeterImpl(accum, "testing")
+
+	counter := metric.Must(meter).NewFloat64Counter("counter.sum")
+
+	_ = metric.Must(meter).NewInt64SumObserver("observer.sum",
+		func(_ context.Context, result metric.Int64ObserverResult) {
+			result.Observe(10, kv.String("K1", "V1"))
+			result.Observe(11, kv.String("K1", "V2"))
+		},
+	)
+
+	counter.Add(ctx, 100, kv.String("K1", "V1"))
+	counter.Add(ctx, 101, kv.String("K1", "V2"))
+
+	accum.Collect(ctx)
+}
+
+func TestProcessorTesting(t *testing.T) {
+	// Test the Processor test helper using a real Accumulator to
+	// generate Accumulations.
+	testProc := processorTest.NewProcessor(
+		processorTest.AggregatorSelector(),
+		label.DefaultEncoder(),
+	)
+	checkpointer := processorTest.Checkpointer(testProc)
+
+	generateTestData(checkpointer)
+
+	expect := map[string]float64{
+		"counter.sum/K1=V1/R=V":  100,
+		"counter.sum/K1=V2/R=V":  101,
+		"observer.sum/K1=V1/R=V": 10,
+		"observer.sum/K1=V2/R=V": 11,
+	}
+
+	// Validate the processor's checkpoint directly.
+	require.EqualValues(t, expect, testProc.Values())
+
+	// Export the data and validate it again.
+	exporter := processorTest.NewExporter(
+		export.PassThroughExporter,
+		label.DefaultEncoder(),
+	)
+
+	err := exporter.Export(context.Background(), checkpointer.CheckpointSet())
+	require.NoError(t, err)
+	require.EqualValues(t, expect, exporter.Values())
+}