Decouple vttest tests from user's config

The screen capture tests were failing on my machine because the screen
capture based vttest tests were using my personal config in
~/.config/aminal/config.toml. This had different colours and a fixed
DPI scaling factor which mean the screen captures didn't match.

The sixel tests were also failing because my login shell is a highly
customised zsh.

A static test config is now passed by the vttest tests and the shell
is set to "/bin/sh" on Linux, OSX etc to help avoid problems due to
differences between shells and shell configs.

config.go

@@ -22,6 +22,13 @@ func getActuallyProvidedFlags() map[string]bool {
 	return result
 }
 
+func maybeGetConfig(override *config.Config) *config.Config {
+	if override != nil {
+		return override
+	}
+	return getConfig()
+}
+
 func getConfig() *config.Config {
 	showVersion := false
 	ignoreConfig := false

main.go

@@ -7,6 +7,7 @@ import (
 	"runtime"
 	"runtime/pprof"
 
+	"github.com/liamg/aminal/config"
 	"github.com/liamg/aminal/gui"
 	"github.com/liamg/aminal/platform"
 	"github.com/liamg/aminal/terminal"
@@ -20,11 +21,12 @@ func init() {
 }
 
 func main() {
-	initialize(nil)
+	initialize(nil, nil)
 }
 
-func initialize(unitTestfunc callback) {
-	conf := getConfig()
+func initialize(unitTestfunc callback, configOverride *config.Config) {
+	conf := maybeGetConfig(configOverride)
+
 	logger, err := getLogger(conf)
 	if err != nil {
 		fmt.Printf("Failed to create logger: %s\n", err)

main_test.go

@@ -6,10 +6,12 @@ import (
 	"flag"
 	"fmt"
 	"os"
+	"runtime"
 	"strings"
 	"testing"
 	"time"
 
+	"github.com/liamg/aminal/config"
 	"github.com/liamg/aminal/gui"
 	"github.com/liamg/aminal/terminal"
 
@@ -123,7 +125,7 @@ func TestCursorMovement(t *testing.T) {
 			g.Close()
 		}
 
-		initialize(testFunc)
+		initialize(testFunc, testConfig())
 	})
 }
 
@@ -159,7 +161,7 @@ func TestScreenFeatures(t *testing.T) {
 			g.Close()
 		}
 
-		initialize(testFunc)
+		initialize(testFunc, testConfig())
 	})
 }
 
@@ -184,7 +186,7 @@ func TestSixel(t *testing.T) {
 			g.Close()
 		}
 
-		initialize(testFunc)
+		initialize(testFunc, testConfig())
 	})
 }
 
@@ -192,3 +194,14 @@ func TestSixel(t *testing.T) {
 func TestExit(t *testing.T) {
 	os.Exit(0)
 }
+
+func testConfig() *config.Config {
+	c := config.DefaultConfig()
+
+	// Use a vanilla shell on POSIX to help ensure consistency.
+	if runtime.GOOS != "windows" {
+		c.Shell = "/bin/sh"
+	}
+
+	return c
+}