Config/Engine: Add data directory to config.json (#549)

* add data directory to config.json

* fix quality check issues

* adjust data directory only when explicitly set

* unexport ValidateSettings
* process flags earlier so they can also be used when loading config
* fix test depends on flags

* rename config.DataDir to DataDirectory

* also don't omit in JSON if empty

* datadir flag induces dry run

* log warning
* enable parallel for sub tests
* leave data dir empty in example config

* remove parallel for loadConfigWithSettings

* create a new config object instead of using a shared one

* remove a test that potentially reads user file

* rename test methods to MixedCaps

* clean up test dir after engine tests

* use global config variable

engine/engine_test.go

@@ -0,0 +1,73 @@
+package engine
+
+import (
+	"os"
+	"testing"
+
+	"github.com/thrasher-corp/gocryptotrader/config"
+)
+
+func TestLoadConfigWithSettings(t *testing.T) {
+	empty := ""
+	somePath := "somePath"
+	// Clean up after the tests
+	defer os.RemoveAll(somePath)
+	tests := []struct {
+		name     string
+		flags    []string
+		settings *Settings
+		want     *string
+		wantErr  bool
+	}{
+		{
+			name: "invalid file",
+			settings: &Settings{
+				ConfigFile: "nonExistent.json",
+			},
+			wantErr: true,
+		},
+		{
+			name: "test file",
+			settings: &Settings{
+				ConfigFile:   config.TestFile,
+				EnableDryRun: true,
+			},
+			want:    &empty,
+			wantErr: false,
+		},
+		{
+			name:  "data dir in settings overrides config data dir",
+			flags: []string{"datadir"},
+			settings: &Settings{
+				ConfigFile:   config.TestFile,
+				DataDir:      somePath,
+				EnableDryRun: true,
+			},
+			want:    &somePath,
+			wantErr: false,
+		},
+	}
+	for _, tt := range tests {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			// prepare the 'flags'
+			flagSet = make(map[string]bool)
+			for _, v := range tt.flags {
+				flagSet[v] = true
+			}
+			// Run the test
+			got, err := loadConfigWithSettings(tt.settings)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("loadConfigWithSettings() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if got != nil || tt.want != nil {
+				if (got == nil && tt.want != nil) || (got != nil && tt.want == nil) {
+					t.Errorf("loadConfigWithSettings() = is nil %v, want nil %v", got == nil, tt.want == nil)
+				} else if got.DataDirectory != *tt.want {
+					t.Errorf("loadConfigWithSettings() = %v, want %v", got.DataDirectory, *tt.want)
+				}
+			}
+		})
+	}
+}