diff --git a/prometheus_client/validation.py b/prometheus_client/validation.py
index cdbba116..e46ce448 100644
--- a/prometheus_client/validation.py
+++ b/prometheus_client/validation.py
@@ -110,7 +110,7 @@ def _validate_labelnames(cls, labelnames):
     for l in labelnames:
         _validate_labelname(l)
         if l in cls._reserved_labelnames:
-            raise ValueError('Reserved label methe fric name: ' + l)
+            raise ValueError('Reserved label metric name: ' + l)
     # Duplicate names collapse distinct label sets during collection.
     duplicates = sorted(name for name, count in Counter(labelnames).items() if count > 1)
     if duplicates:
@@ -126,4 +126,4 @@ def _validate_exemplar(exemplar):
         runes += len(k)
         runes += len(v)
     if runes > 128:
-        raise ValueError('Exemplar labels have %d UTF-8 characters, exceeding the limit of 128')
+        raise ValueError(f'Exemplar labels have {runes} UTF-8 characters, exceeding the limit of 128')
diff --git a/tests/test_core.py b/tests/test_core.py
index 2c29f79a..50ba18a4 100644
--- a/tests/test_core.py
+++ b/tests/test_core.py
@@ -133,12 +133,13 @@ def test_exemplar_unicode(self):
 
     def test_exemplar_too_long(self):
         # 129 characters should fail.
-        self.assertRaises(ValueError, self.counter.inc, exemplar={
-            'abcdefghijklmnopqrstuvwxyz': '26+16 characters',
-            'x1234567': '8+15 characters',
-            'zyxwvutsrqponmlkjihgfedcba': '26+16 characters',
-            'y123456': '7+15 characters',
-        })
+        with self.assertRaisesRegex(ValueError, 'Exemplar labels have 129 UTF-8 characters'):
+            self.counter.inc(exemplar={
+                'abcdefghijklmnopqrstuvwxyz': '26+16 characters',
+                'x1234567': '8+15 characters',
+                'zyxwvutsrqponmlkjihgfedcba': '26+16 characters',
+                'y123456': '7+15 characters',
+            })
 
 
 class TestDisableCreated(unittest.TestCase):
@@ -461,7 +462,8 @@ def test_setting_buckets(self):
         self.assertRaises(ValueError, Histogram, 'h', 'help', registry=None, buckets=[3, 1])
 
     def test_labels(self):
-        self.assertRaises(ValueError, Histogram, 'h', 'help', registry=None, labelnames=['le'])
+        with self.assertRaisesRegex(ValueError, 'Reserved label metric name: le'):
+            Histogram('h', 'help', registry=None, labelnames=['le'])
 
         self.labels.labels('a').observe(2)
         self.assertEqual(0, self.registry.get_sample_value('hl_bucket', {'le': '1.0', 'l': 'a'}))
@@ -534,12 +536,13 @@ def test_exemplar_invalid_label_name(self):
 
     def test_exemplar_too_long(self):
         # 129 characters in total should fail.
-        self.assertRaises(ValueError, self.histogram.observe, 1.0, exemplar={
-            'abcdefghijklmnopqrstuvwxyz': '26+16 characters',
-            'x1234567': '8+15 characters',
-            'zyxwvutsrqponmlkjihgfedcba': '26+16 characters',
-            'y123456': '7+15 characters',
-        })
+        with self.assertRaisesRegex(ValueError, 'Exemplar labels have 129 UTF-8 characters'):
+            self.histogram.observe(1.0, exemplar={
+                'abcdefghijklmnopqrstuvwxyz': '26+16 characters',
+                'x1234567': '8+15 characters',
+                'zyxwvutsrqponmlkjihgfedcba': '26+16 characters',
+                'y123456': '7+15 characters',
+            })
 
 
 class TestInfo(unittest.TestCase):
@@ -787,7 +790,8 @@ def test_invalid_names_raise(self):
         self.assertRaises(ValueError, Counter, '', 'help', namespace='&')
         self.assertRaises(ValueError, Counter, '', 'help', subsystem='(')
         self.assertRaises(ValueError, Counter, 'c_total', '', labelnames=['__reserved'])
-        self.assertRaises(ValueError, Summary, 'c_total', '', labelnames=['quantile'])
+        with self.assertRaisesRegex(ValueError, 'Reserved label metric name: quantile'):
+            Summary('c_total', '', labelnames=['quantile'])
 
     def test_duplicate_labelnames_raise_before_registration(self):
         # Repeated names would collapse distinct label sets on export.