Add exec.Command stub mechanism that matches by arguments

mislav · mislav · commit f9783fe812da · 2020-09-23T18:38:29.000+02:00
Our previous command stub mechanism matches stubs sequentially, which leads to brittle tests when the exec calls get reordered or removed in the implementation.
diff --git a/internal/run/stub.go b/internal/run/stub.go
@@ -0,0 +1,91 @@
+package run
+
+import (
+	"fmt"
+	"os/exec"
+	"regexp"
+	"strings"
+)
+
+type T interface {
+	Helper()
+	Errorf(string, ...interface{})
+}
+
+func Stub() (*CommandStubber, func(T)) {
+	cs := &CommandStubber{}
+	teardown := SetPrepareCmd(func(cmd *exec.Cmd) Runnable {
+		s := cs.find(cmd.Args)
+		if s == nil {
+			panic(fmt.Sprintf("no exec stub for `%s`", strings.Join(cmd.Args, " ")))
+		}
+		for _, c := range s.callbacks {
+			c(cmd.Args)
+		}
+		s.matched = true
+		return s
+	})
+
+	return cs, func(t T) {
+		defer teardown()
+		var unmatched []string
+		for _, s := range cs.stubs {
+			if s.matched {
+				continue
+			}
+			unmatched = append(unmatched, s.pattern.String())
+		}
+		if len(unmatched) == 0 {
+			return
+		}
+		t.Helper()
+		t.Errorf("umatched stubs (%d): %s", len(unmatched), strings.Join(unmatched, ", "))
+	}
+}
+
+type CommandStubber struct {
+	stubs []*commandStub
+}
+
+func (cs *CommandStubber) Register(p string, exitStatus int, output string, callbacks ...CommandCallback) {
+	cs.stubs = append(cs.stubs, &commandStub{
+		pattern:    regexp.MustCompile(p),
+		exitStatus: exitStatus,
+		stdout:     output,
+		callbacks:  callbacks,
+	})
+}
+
+func (cs *CommandStubber) find(args []string) *commandStub {
+	line := strings.Join(args, " ")
+	for _, s := range cs.stubs {
+		if !s.matched && s.pattern.MatchString(line) {
+			return s
+		}
+	}
+	return nil
+}
+
+type CommandCallback func([]string)
+
+type commandStub struct {
+	pattern    *regexp.Regexp
+	matched    bool
+	exitStatus int
+	stdout     string
+	callbacks  []CommandCallback
+}
+
+func (s *commandStub) Run() error {
+	if s.exitStatus != 0 {
+		return fmt.Errorf("%s exited with status %d", s.pattern, s.exitStatus)
+	}
+	return nil
+}
+
+func (s *commandStub) Output() ([]byte, error) {
+	if s.exitStatus != 0 {
+		return []byte(nil), fmt.Errorf("%s exited with status %d", s.pattern, s.exitStatus)
+	}
+	return []byte(s.stdout), nil
+}
