fix up tests

This fixes up some git and oscommand tests, and pulls some tests into commit_list_builder_test.go

I've also made the NewDummyBlah functions public so that I didn't need to duplicate them across packages
I've also given OSCommand a SetCommand() method for setting the command on the struct
I've also created a file utils.go in the test package for creating convient 'CommandSwapper's, which
basically enable you to assert a sequence of commands on the command line, and swap each one out for
a different one to actually be executed

pkg/commands/dummies.go

@@ -0,0 +1,58 @@
+package commands
+
+import (
+	"io/ioutil"
+
+	"github.com/jesseduffield/lazygit/pkg/config"
+	"github.com/jesseduffield/lazygit/pkg/i18n"
+	"github.com/sirupsen/logrus"
+	"github.com/spf13/viper"
+	yaml "gopkg.in/yaml.v2"
+)
+
+// This file exports dummy constructors for use by tests in other packages
+
+// NewDummyOSCommand creates a new dummy OSCommand for testing
+func NewDummyOSCommand() *OSCommand {
+	return NewOSCommand(NewDummyLog(), NewDummyAppConfig())
+}
+
+// NewDummyAppConfig creates a new dummy AppConfig for testing
+func NewDummyAppConfig() *config.AppConfig {
+	appConfig := &config.AppConfig{
+		Name:        "lazygit",
+		Version:     "unversioned",
+		Commit:      "",
+		BuildDate:   "",
+		Debug:       false,
+		BuildSource: "",
+		UserConfig:  viper.New(),
+	}
+	_ = yaml.Unmarshal([]byte{}, appConfig.AppState)
+	return appConfig
+}
+
+// NewDummyLog creates a new dummy Log for testing
+func NewDummyLog() *logrus.Entry {
+	log := logrus.New()
+	log.Out = ioutil.Discard
+	return log.WithField("test", "test")
+}
+
+// NewDummyGitCommand creates a new dummy GitCommand for testing
+func NewDummyGitCommand() *GitCommand {
+	return NewDummyGitCommandWithOSCommand(NewDummyOSCommand())
+}
+
+// NewDummyGitCommandWithOSCommand creates a new dummy GitCommand for testing
+func NewDummyGitCommandWithOSCommand(osCommand *OSCommand) *GitCommand {
+	return &GitCommand{
+		Log:                NewDummyLog(),
+		OSCommand:          osCommand,
+		Tr:                 i18n.NewLocalizer(NewDummyLog()),
+		Config:             NewDummyAppConfig(),
+		getGlobalGitConfig: func(string) (string, error) { return "", nil },
+		getLocalGitConfig:  func(string) (string, error) { return "", nil },
+		removeFile:         func(string) error { return nil },
+	}
+}