Add ensure.RunParallel

ensuring/run.go

@@ -2,7 +2,7 @@ package ensuring
 
 import "github.com/JosiahWitt/ensure/internal/testctx"
 
-// Run fn as a subtest called name.
+// Run runs fn as a subtest called name, using [testing.T.Run].
 func (e E) Run(name string, fn func(ensure E)) {
 	c := e(nil)
 	c.t.Helper()
@@ -15,3 +15,21 @@ func (e E) Run(name string, fn func(ensure E)) {
 		fn(ensure)
 	})
 }
+
+// RunParallel runs fn as a subtest called name, using [testing.T.Run].
+// It calls [testing.T.Parallel] just before calling fn, causing fn to
+// be run in parallel with (and only with) other parallel tests. See
+// the [testing.T.Parallel] docs for more info.
+func (e E) RunParallel(name string, fn func(ensure E)) {
+	c := e(nil)
+	c.t.Helper()
+	c.markRun()
+
+	c.ctx.Run(name, func(ctx testctx.Context) {
+		t := ctx.T()
+		t.Helper()
+		ensure := wrap(t)
+		t.Parallel()
+		fn(ensure)
+	})
+}

ensuring/run_test.go

@@ -12,6 +12,20 @@ import (
 )
 
 func TestERun(t *testing.T) {
+	testERun(t, false, func(ensure ensuring.E) func(string, func(ensuring.E)) {
+		return ensure.Run
+	})
+}
+
+func TestERunParallel(t *testing.T) {
+	testERun(t, true, func(ensure ensuring.E) func(string, func(ensuring.E)) {
+		return ensure.RunParallel
+	})
+}
+
+type runBuilderFunc func(ensure ensuring.E) func(string, func(ensuring.E))
+
+func testERun(t *testing.T, isParallel bool, runBuilder runBuilderFunc) {
 	ctrl := gomock.NewController(t)
 
 	outerMockT := setupMockTWithCleanupCheck(t)
@@ -23,6 +37,10 @@ func TestERun(t *testing.T) {
 	innerMockT := setupMockTWithCleanupCheck(t)
 	innerMockT.EXPECT().Helper().Times(2)
 
+	if isParallel {
+		innerMockT.EXPECT().Parallel()
+	}
+
 	innerMockCtx := mock_testctx.NewMockContext(ctrl)
 	innerMockCtx.EXPECT().T().Return(innerMockT)
 	testhelper.SetTestContext(t, innerMockT, innerMockCtx)
@@ -36,7 +54,8 @@ func TestERun(t *testing.T) {
 
 	var innerEnsure ensuring.E
 	outerEnsure := ensure.New(outerMockT)
-	outerEnsure.Run(name, func(ensure ensuring.E) {
+	run := runBuilder(outerEnsure)
+	run(name, func(ensure ensuring.E) {
 		innerEnsure = ensure
 	})
 

internal/testctx/testctx.go

@@ -15,6 +15,7 @@ type T interface {
 	Run(name string, f func(t *testing.T)) bool
 	Helper()
 	Cleanup(func())
+	Parallel()
 }
 
 var _ T = &testing.T{}