Stacking lines of text in a LineLegend?

Question

I have the following LineLegend:

Labeled[
 Plot[Exp[-0.03*t], {t, 0, 100}, Frame -> True]
 , LineLegend[{Blue, Green, Red}
  , {"a = test1
    a = test2"
   , "a = test3 
    a = test4", "a = test5 
    a = test6"}
  , LegendLayout -> "Row"
  , LegendMarkers -> {
    {"\[FilledCircle]", 15}, {"\[FilledUpTriangle]", 
     15}, {"\[FilledSquare]", 15}
    }
  ]
 ]

I tried to stack, e.g., a = test1 and a = test2 in a column but keep the overall legend presented as a row by pressing the Enter key between a = test1 and a = test2, but not only did it not work, it seemed like a hacky way of solving the problem.

Is there a way to stack legend item text while maintaining a "Row" layout?

Answer 1

Labeled[Plot[Exp[-0.03*t], {t, 0, 100}, Frame -> True]
 , LineLegend[ {Blue, Green, Red},
  {"a = test1\na = test2"
   , "a = test3\na = test4"
   , "a = test5\na = test6"}
  , LegendLayout -> {"Row", 1}
  , LegendMarkers -> {{"\[FilledCircle]", 15}, {"\[FilledUpTriangle]",
      15}, {"\[FilledSquare]", 15}}]
 ]

---

EDIT

Is there a way to center the marker ...?

I will request you to explore some possibilities.

SeedRandom[1];
Labeled[Plot[Exp[-0.03*t], {t, 0, 100}, Frame -> True]
 , LineLegend[ {Blue, Green, Red},
  Framed[Style[#, RandomColor[]], FrameStyle -> Red] & /@ {
    "a = test1\na = test2"
    , "a = test3\na = test4"
    , "a = test5\na = test6"}
  , LegendLayout -> {"Row", 1}
  , LegendMarkers -> {{"\[FilledCircle]", 15}, {"\[FilledUpTriangle]",
      15}, {"\[FilledSquare]", 15}}
  , LegendFunction -> (Framed[#, RoundingRadius -> 4, 
      FrameStyle -> Darker@Green, Alignment -> Top] &)
  ]
 , Top
 ]