matplotlib
diff --git a/‎lib/matplotlib/tests/test_ticker.py
Copy file name to clipboardExpand all lines: lib/matplotlib/tests/test_ticker.py
+37-9Lines changed: 37 additions & 9 deletions b/‎lib/matplotlib/tests/test_ticker.py
Copy file name to clipboardExpand all lines: lib/matplotlib/tests/test_ticker.py
+37-9Lines changed: 37 additions & 9 deletions
@@ -1594,19 +1594,47 @@ def test_engformatter_usetex_useMathText():
         assert x_tick_label_text == ['$0$', '$500$', '$1$ k']
 
 
-def test_engformatter_useOffset():
+@pytest.mark.parametrize(
+    'oom_center, oom_noise', [
+        (15, 6),
+        (12, 3),
+        (9, 3),
+        (9, 6),
+        (0, -6),
+        # Going to lower orders of magnitudes will make this test fail due to
+        # floating points approximated as zero. Putting 12 and above oom difference
+        # between center and the noise will also fail, due to ticks give different
+        # unit prefixes
+    ]
+)
+def test_engformatter_offset(oom_center, oom_noise):
+    UNIT = "eV"
+    # Intentionally picking also negative numbers
+    r = range(-2, 9)
     fig, ax = plt.subplots()
-    data_offset = 10000000
-    ydata = range(data_offset, data_offset+5)
+    data_offset = 10**oom_center
+    ydata = data_offset + np.array(r, dtype=float)*10**oom_noise
     ax.plot(ydata)
     ax.set_yticks(ydata)
-    ax.yaxis.set_major_formatter(mticker.EngFormatter(useOffset=True, unit="Hz"))
+    formatter = mticker.EngFormatter(useOffset=True, unit=UNIT)
+    ax.yaxis.set_major_formatter(formatter)
     fig.canvas.draw()
-    y_tick_label_text = [labl.get_text() for labl in ax.get_yticklabels()]
-    offset = ax.yaxis.get_major_formatter().get_offset()
-    expectedTicks = list(map("{} Hz".format, np.array(ydata) - data_offset))
-    assert y_tick_label_text == expectedTicks
-    assert "+10 MHz" == offset
+    ticksGot = [labl.get_text() for labl in ax.get_yticklabels()]
+    ticksExpected = list(map(
+        # Fix negative number's - sign in case unicode is used
+        lambda n: formatter.fix_minus(str(n)) + " " + (
+            # zero is zero, no matter what is the oom
+            formatter.ENG_PREFIXES[oom_noise] if n != 0 else ""
+        ) + UNIT,
+        r
+    ))
+    offsetGot = ax.yaxis.get_major_formatter().get_offset()
+    offsetExpected = "+1 {}{}".format(
+        formatter.ENG_PREFIXES[oom_center],
+        UNIT
+    )
+    assert ticksGot == ticksExpected
+    assert offsetExpected == offsetGot
 
 
 class TestPercentFormatter: