Clarify labels (#69)

The label will follow the format `label[:schema[:args]]`, and the schema will be `host` if it's omitted. So

- `ubuntu:docker://node:18`: Run jobs with label `ubuntu` via docker with image `node:18`
- `ubuntu:host`: Run jobs with label `ubuntu` on the host directly.
- `ubuntu`: Same as `ubuntu:host`.
- `ubuntu:vm:ubuntu-latest`: (Just a example, not Implemented) Run jobs with label `ubuntu` via virtual machine with iso `ubuntu-latest`.

Reviewed-on: https://gitea.com/gitea/act_runner/pulls/69
Reviewed-by: Zettat123 <zettat123@noreply.gitea.io>
Reviewed-by: wxiaoguang <wxiaoguang@noreply.gitea.io>

runtime/label_test.go

@@ -0,0 +1,60 @@
+package runtime
+
+import "testing"
+
+func TestParseLabel(t *testing.T) {
+	tests := []struct {
+		args       string
+		wantLabel  string
+		wantSchema string
+		wantArg    string
+		wantErr    bool
+	}{
+		{
+			args:       "ubuntu:docker://node:18",
+			wantLabel:  "ubuntu",
+			wantSchema: "docker",
+			wantArg:    "//node:18",
+			wantErr:    false,
+		},
+		{
+			args:       "ubuntu:host",
+			wantLabel:  "ubuntu",
+			wantSchema: "host",
+			wantArg:    "",
+			wantErr:    false,
+		},
+		{
+			args:       "ubuntu",
+			wantLabel:  "ubuntu",
+			wantSchema: "host",
+			wantArg:    "",
+			wantErr:    false,
+		},
+		{
+			args:       "ubuntu:vm:ubuntu-18.04",
+			wantLabel:  "",
+			wantSchema: "",
+			wantArg:    "",
+			wantErr:    true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.args, func(t *testing.T) {
+			gotLabel, gotSchema, gotArg, err := ParseLabel(tt.args)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("parseLabel() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if gotLabel != tt.wantLabel {
+				t.Errorf("parseLabel() gotLabel = %v, want %v", gotLabel, tt.wantLabel)
+			}
+			if gotSchema != tt.wantSchema {
+				t.Errorf("parseLabel() gotSchema = %v, want %v", gotSchema, tt.wantSchema)
+			}
+			if gotArg != tt.wantArg {
+				t.Errorf("parseLabel() gotArg = %v, want %v", gotArg, tt.wantArg)
+			}
+		})
+	}
+}