Add ffmpeg virtual tests

internal/ffmpeg/virtual/virtual_test.go

@@ -0,0 +1,20 @@
+package virtual
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestGetInput(t *testing.T) {
+	s := GetInput("video")
+	require.Equal(t, "-re -f lavfi -i testsrc=decimals=2:size=1920x1080", s)
+
+	s = GetInput("video=testsrc2&size=4K")
+	require.Equal(t, "-re -f lavfi -i testsrc2=size=3840x2160", s)
+}
+
+func TestGetInputTTS(t *testing.T) {
+	s := GetInputTTS("text=hello world&voice=slt")
+	require.Equal(t, `-re -f lavfi -i "flite=text='hello world':voiceslt"`, s)
+}