testing: add Testing function

This is new in Go 1.21.

builder/build.go

@@ -217,19 +217,27 @@ func Build(pkgName, outpath, tmpdir string, config *compileopts.Config) (BuildRe
 	var packageJobs []*compileJob
 	packageActionIDJobs := make(map[string]*compileJob)
 
+	if config.Options.GlobalValues == nil {
+		config.Options.GlobalValues = make(map[string]map[string]string)
+	}
 	if config.Options.GlobalValues["runtime"]["buildVersion"] == "" {
 		version := goenv.Version
 		if strings.HasSuffix(goenv.Version, "-dev") && goenv.GitSha1 != "" {
 			version += "-" + goenv.GitSha1
 		}
-		if config.Options.GlobalValues == nil {
-			config.Options.GlobalValues = make(map[string]map[string]string)
-		}
 		if config.Options.GlobalValues["runtime"] == nil {
 			config.Options.GlobalValues["runtime"] = make(map[string]string)
 		}
 		config.Options.GlobalValues["runtime"]["buildVersion"] = version
 	}
+	if config.TestConfig.CompileTestBinary {
+		// The testing.testBinary is set to "1" when in a test.
+		// This is needed for testing.Testing() to work correctly.
+		if config.Options.GlobalValues["testing"] == nil {
+			config.Options.GlobalValues["testing"] = make(map[string]string)
+		}
+		config.Options.GlobalValues["testing"]["testBinary"] = "1"
+	}
 
 	var embedFileObjects []*compileJob
 	for _, pkg := range lprogram.Sorted() {

src/testing/testing.go

@@ -120,6 +120,15 @@ func Verbose() bool {
 	return flagVerbose
 }
 
+// String constant that is being set when running a test.
+var testBinary string
+
+// Testing returns whether the program was compiled as a test, using "tinygo
+// test". It returns false when built using "tinygo build", "tinygo flash", etc.
+func Testing() bool {
+	return testBinary == "1"
+}
+
 // flushToParent writes c.output to the parent after first writing the header
 // with the given format and arguments.
 func (c *common) flushToParent(testName, format string, args ...interface{}) {

src/testing/testing_test.go

@@ -195,3 +195,9 @@ func TestSetenv(t *testing.T) {
 		}
 	}
 }
+
+func TestTesting(t *testing.T) {
+	if !testing.Testing() {
+		t.Error("Expected testing.Testing() to return true while in a test")
+	}
+}

testdata/testing.go

@@ -73,6 +73,9 @@ func fakeMatchString(pat, str string) (bool, error) {
 }
 
 func main() {
+	if testing.Testing() {
+		println("not running a test at the moment, testing.Testing() should return false")
+	}
 	testing.Init()
 	flag.Set("test.run", ".*/B")
 	m := testing.MainStart(matchStringOnly(fakeMatchString /*regexp.MatchString*/), tests, benchmarks, fuzzes, examples)