diff --git a/tests/func/test_dvcfile.py b/tests/func/test_dvcfile.py
index 6206f12e38..5f3483c376 100644
--- a/tests/func/test_dvcfile.py
+++ b/tests/func/test_dvcfile.py
@@ -2,7 +2,7 @@
 
 import pytest
 
-from dvc.dvcfile import PIPELINE_FILE, PIPELINE_LOCK, Dvcfile
+from dvc.dvcfile import PIPELINE_FILE, PIPELINE_LOCK, Dvcfile, SingleStageFile
 from dvc.stage.exceptions import (
     StageFileDoesNotExistError,
     StageFileFormatError,
@@ -59,8 +59,9 @@ def test_run_load_one_on_single_stage(tmp_dir, dvc):
         always_changed=True,
         single_stage=True,
     )
-    assert Dvcfile(dvc, stage.path).stages.get("random-name")
-    assert Dvcfile(dvc, stage.path).stage
+    assert isinstance(Dvcfile(dvc, stage.path), SingleStageFile)
+    assert Dvcfile(dvc, stage.path).stages.get("random-name") == stage
+    assert Dvcfile(dvc, stage.path).stage == stage
 
 
 def test_has_stage_with_name(tmp_dir, dvc):
@@ -110,23 +111,14 @@ def test_load_all_singlestage(tmp_dir, dvc):
         always_changed=True,
         single_stage=True,
     )
-    stages = Dvcfile(dvc, "foo2.dvc").stages.values()
+    dvcfile = Dvcfile(dvc, "foo2.dvc")
+    assert isinstance(dvcfile, SingleStageFile)
+    assert len(dvcfile.stages) == 1
+    stages = dvcfile.stages.values()
     assert len(stages) == 1
     assert list(stages) == [stage1]
 
 
-def test_load_singlestage(tmp_dir, dvc):
-    tmp_dir.gen("foo", "foo")
-    stage1 = dvc.run(
-        cmd="cp foo foo2",
-        deps=["foo"],
-        metrics=["foo2"],
-        always_changed=True,
-        single_stage=True,
-    )
-    assert Dvcfile(dvc, "foo2.dvc").stage == stage1
-
-
 def test_try_get_single_stage_from_pipeline_file(tmp_dir, dvc):
     from dvc.dvcfile import DvcException
 
diff --git a/tests/unit/test_dvcfile.py b/tests/unit/test_dvcfile.py
index 41982e5ca2..3668ee2090 100644
--- a/tests/unit/test_dvcfile.py
+++ b/tests/unit/test_dvcfile.py
@@ -1,6 +1,19 @@
 import pytest
 
-from dvc.dvcfile import Dvcfile, PipelineFile, SingleStageFile
+from dvc.dvcfile import (
+    PIPELINE_FILE,
+    PIPELINE_LOCK,
+    Dvcfile,
+    PipelineFile,
+    SingleStageFile,
+)
+from dvc.stage import PipelineStage
+from dvc.stage.exceptions import (
+    StageFileDoesNotExistError,
+    StageFileFormatError,
+    StageFileIsNotDvcFileError,
+)
+from dvc.utils.yaml import dump_yaml
 
 
 @pytest.mark.parametrize(
@@ -24,3 +37,45 @@ def test_pipelines_file(path):
 def test_pipelines_single_stage_file(path):
     file_obj = Dvcfile(object(), path)
     assert isinstance(file_obj, SingleStageFile)
+
+
+@pytest.mark.parametrize("file", ["stage.dvc", "dvc.yaml"])
+def test_stage_load_on_not_existing_file(tmp_dir, dvc, file):
+    dvcfile = Dvcfile(dvc, file)
+    assert not dvcfile.exists()
+    with pytest.raises(StageFileDoesNotExistError):
+        assert dvcfile.stages.values()
+    (tmp_dir / file).mkdir()
+    with pytest.raises(StageFileIsNotDvcFileError):
+        assert dvcfile.stages.values()
+
+
+@pytest.mark.parametrize("file", ["stage.dvc", "dvc.yaml"])
+def test_stage_load_on_invalid_data(tmp_dir, dvc, file):
+    data = {"is_this_a_valid_dvcfile": False}
+    dump_yaml(file, data)
+    dvcfile = Dvcfile(dvc, file)
+    with pytest.raises(StageFileFormatError):
+        assert dvcfile.stages
+    with pytest.raises(StageFileFormatError):
+        assert dvcfile.validate(data, file)
+
+
+def test_dump_stage(tmp_dir, dvc):
+    stage = PipelineStage(
+        dvc, cmd="command", name="stage_name", path="dvc.yaml"
+    )
+    dvcfile = Dvcfile(dvc, "dvc.yaml")
+
+    dvcfile.dump(stage, no_lock=True)
+    assert not (tmp_dir / PIPELINE_FILE).exists()
+    assert not (tmp_dir / PIPELINE_LOCK).exists()
+
+    dvcfile.dump(stage, no_lock=False)
+    assert not (tmp_dir / PIPELINE_FILE).exists()
+    assert dvcfile._lockfile.load()
+
+    dvcfile.dump(stage, update_pipeline=True, no_lock=False)
+    assert (tmp_dir / PIPELINE_FILE).exists()
+    assert (tmp_dir / PIPELINE_LOCK).exists()
+    assert list(dvcfile.stages.values()) == [stage]