feat: add support for pretty/nix format

improve handling string test values

cmd/nixtest/main.go

@@ -110,6 +110,15 @@ func shouldSkip(input string, pattern string) bool {
 	return regex.MatchString(input)
 }
 
+func isString(value any) bool {
+	switch value.(type) {
+	case string:
+		return true
+	default:
+		return false
+	}
+}
+
 func runTest(spec TestSpec) TestResult {
 	startTime := time.Now()
 	result := TestResult{
@@ -168,22 +177,32 @@ func runTest(spec TestSpec) TestResult {
 	if reflect.DeepEqual(actual, expected) {
 		result.Status = StatusSuccess
 	} else {
-		text1, err := json.MarshalIndent(expected, "", "  ")
-		if err != nil {
-			result.Status = StatusError
-			result.ErrorMessage = fmt.Sprintf("[system] failed to json marshal 'expected': %v", err.Error())
-			goto end
-		}
-		text2, err := json.MarshalIndent(actual, "", "  ")
-		if err != nil {
-			result.Status = StatusError
-			result.ErrorMessage = fmt.Sprintf("[system] failed to json marshal 'actual': %v", err.Error())
-			goto end
+		var text1, text2 string
+
+		// just keep strings as is, only json marshal if any of them is not a string
+		if isString(actual) && isString(expected) {
+			text1 = actual.(string)
+			text2 = expected.(string)
+		} else {
+			bytes1, err := json.MarshalIndent(expected, "", "  ")
+			if err != nil {
+				result.Status = StatusError
+				result.ErrorMessage = fmt.Sprintf("[system] failed to json marshal 'expected': %v", err.Error())
+				goto end
+			}
+			bytes2, err := json.MarshalIndent(actual, "", "  ")
+			if err != nil {
+				result.Status = StatusError
+				result.ErrorMessage = fmt.Sprintf("[system] failed to json marshal 'actual': %v", err.Error())
+				goto end
+			}
+			text1 = string(bytes1)
+			text2 = string(bytes2)
 		}
 
 		result.Status = StatusFailure
-		result.Expected = string(text1)
-		result.Actual = string(text2)
+		result.Expected = text1
+		result.Actual = text2
 	}
 
 end:

flake.nix

@@ -77,6 +77,7 @@
                 pos = __curPos;
                 expected = null;
                 actualDrv = pkgs.runCommand "test-error-drv" {} ''
+                  echo "This works, but its better to just write 'fail' to \$out and expect 'success' or sth."
                   exit 1
                 '';
               }
@@ -88,6 +89,17 @@
                 pos = __curPos;
                 actual = {hello = "world";};
               }
+              {
+                name = "pretty-snapshot";
+                type = "snapshot";
+                format = "pretty";
+                actual = {
+                  example = args: {};
+                  example2 = {
+                    drv = pkgs.hello;
+                  };
+                };
+              }
               {
                 name = "test-drv";
                 pos = __curPos;

lib/default.nix

@@ -8,14 +8,20 @@
     type ? "unit",
     name,
     description ? "",
+    format ? "json",
     expected ? null,
     actual ? null,
     actualDrv ? null,
     pos ? null,
   }: let
     fileRelative = lib.removePrefix ((toString self) + "/") pos.file;
+    actual' =
+      if format == "json"
+      then actual
+      else lib.generators.toPretty {} actual;
   in {
-    inherit type name description expected actual;
+    inherit type name description expected;
+    actual = actual';
     # discard string context, otherwise it's being built instantly which we don't want
     actualDrv = builtins.unsafeDiscardStringContext (actualDrv.drvPath or "");
     pos =

snapshots/pretty-snapshot.snap.json

@@ -0,0 +1 @@
+"{\n  example = \u003cfunction\u003e;\n  example2 = {\n    drv = \u003cderivation hello-2.12.1\u003e;\n  };\n}"