api: Add exp_show.

Closes #8775
Closes #7167

tests/func/api/test_experiments.py

@@ -2,9 +2,10 @@ import pytest
 
 from dvc import api
 from dvc.repo.experiments.exceptions import ExperimentExistsError
+from tests.unit.repo.experiments.conftest import exp_stage  # noqa: F401
 
 
-def test_exp_save(tmp_dir, dvc, scm, mocker):
+def test_exp_save(tmp_dir, dvc, scm):
     tmp_dir.scm_gen({"foo": "foo"}, commit="initial")
 
     api.exp_save()
@@ -16,3 +17,16 @@ def test_exp_save(tmp_dir, dvc, scm, mocker):
     ):
         api.exp_save("foo")
     api.exp_save("foo", force=True)
+
+
+def test_exp_show(tmp_dir, dvc, scm, exp_stage):  # noqa: F811
+    exps = api.exp_show()
+
+    assert len(exps) == 2
+    assert isinstance(exps, list)
+    assert isinstance(exps[0], dict)
+    assert isinstance(exps[1], dict)
+    # Postprocessing casting to float
+    assert exps[0]["metrics.yaml:foo"] == 1.0
+    # Postprocessing using `None` as fill value
+    assert exps[0]["State"] is None