Added file save checks for renderers (#260)

Added a test to verify that the Matplotlib and Text renderers save circuit files in PNG and TXT formats. The test checks file creation using the tmpdir fixture for multiple QC fixtures.

tests/test_renderer.py

@@ -170,5 +170,27 @@ def test_matrenderer(request, qc_fixture):
     """
     qc = request.getfixturevalue(qc_fixture)
 
-    with patch("matplotlib.pyplot.show"):
+    with patch("matplotlib.pyplot.show"):  # to avoid showing the plot
         qc.draw("matplotlib")
+
+
+@pytest.mark.parametrize("qc_fixture", ["qc1", "qc2", "qc3"])
+def test_circuit_saving(request, qc_fixture, tmpdir):
+    """
+    Test if the different renderers can save the circuit in different formats.
+    """
+
+    qc = request.getfixturevalue(qc_fixture)
+
+    # test MatRenderer
+    with patch("matplotlib.pyplot.show"):  # to avoid showing the plot
+        qc.draw("matplotlib", save=True, file_path=str(tmpdir.join("test")))
+    assert tmpdir.join(
+        "test.png"
+    ).check(), "MatRenderer saved PNG file not found."
+
+    # test TextRenderer
+    qc.draw("text", save=True, file_path=str(tmpdir.join("test")))
+    assert tmpdir.join(
+        "test.txt"
+    ).check(), "TextRenderer saved TXT file not found."