Add more test for custom fakers

src/test/java/net/datafaker/providers/base/CustomFakerTest.java

@@ -1,5 +1,6 @@
 package net.datafaker.providers.base;
 
+import net.datafaker.annotations.Deterministic;
 import org.junit.jupiter.api.RepeatedTest;
 import org.junit.jupiter.api.Test;
 
@@ -155,4 +156,103 @@ void weightedInsectNameTest() {
         assertThat(insectCounts.get("Driver ant")).as(() -> "Insects: " + insectCounts).isGreaterThan(insectCounts.get("Fire ant"));
         assertThat(insectCounts.get("Fire ant")).as(() -> "Insects: " + insectCounts).isGreaterThan(insectCounts.get("Harvester ant"));
     }
+
+    public static final class HolderA {
+        public static final class WidgetCustomTestFaker extends AbstractProvider<BaseProviders> {
+            public WidgetCustomTestFaker(BaseProviders faker) {
+                super(faker);
+            }
+
+            @Deterministic
+            public String value() {
+                return "A-widget";
+            }
+        }
+    }
+
+    public static final class HolderB {
+        public static final class WidgetCustomTestFaker extends AbstractProvider<BaseProviders> {
+            public WidgetCustomTestFaker(BaseProviders faker) {
+                super(faker);
+            }
+
+            @Deterministic
+            public String value() {
+                return "B-widget";
+            }
+        }
+    }
+
+    public static final class FakerA extends BaseFaker {
+        public FakerA() {
+            super(Locale.ENGLISH);
+        }
+
+        public HolderA.WidgetCustomTestFaker widget() {
+            return getProvider(HolderA.WidgetCustomTestFaker.class, HolderA.WidgetCustomTestFaker::new);
+        }
+    }
+
+    public static final class FakerB extends BaseFaker {
+        public FakerB() {
+            super(Locale.ENGLISH);
+        }
+
+        public HolderB.WidgetCustomTestFaker widget() {
+            return getProvider(HolderB.WidgetCustomTestFaker.class, HolderB.WidgetCustomTestFaker::new);
+        }
+    }
+
+    public static final class HolderG {
+        public static final class GizmoCustomTestFaker extends AbstractProvider<BaseProviders> {
+            public GizmoCustomTestFaker(BaseProviders faker) {
+                super(faker);
+            }
+
+            @Deterministic
+            public String value() {
+                return "G-value";
+            }
+        }
+    }
+
+    public static final class FakerG extends BaseFaker {
+        public FakerG() {
+            super(Locale.ENGLISH);
+        }
+
+        public HolderG.GizmoCustomTestFaker gizmo() {
+            return getProvider(HolderG.GizmoCustomTestFaker.class, HolderG.GizmoCustomTestFaker::new);
+        }
+    }
+
+    @Test
+    void recipeMustNotLeakAcrossRootsWithSameSimpleProviderName() {
+        // Need for multiple iteration because of possible cache issues
+        for (int i = 0; i < 100; i++) {
+            FakerA a = new FakerA();
+            FakerB b = new FakerB();
+
+            // Sanity: each faker resolves its own provider correctly in isolation.
+            assertThat(a.expression("#{Widget.value}")).isEqualTo("A-widget"); // populates static recipe
+
+            // HolderA.Widget#value against a HolderB.Widget instance.
+            assertThat(b.expression("#{Widget.value}")).isEqualTo("B-widget");
+        }
+    }
+
+    @Test
+    void recipeMustNotNpeWhenOtherRootLacksTheProvider() {
+        // Need for multiple iteration because of possible cache issues
+        for (int i = 0; i < 100; i++) {
+            FakerG withGizmo = new FakerG();
+            BaseFaker plain = new BaseFaker(Locale.ENGLISH);
+
+            assertThat(withGizmo.expression("#{Gizmo.value}")).isEqualTo("G-value"); // populates static recipe
+
+            assertThatThrownBy(() -> plain.expression("#{Gizmo.value}"))
+                .isInstanceOf(RuntimeException.class)
+                .hasMessageContaining("Unable to resolve");
+        }
+    }
 }

src/test/java/net/datafaker/script/ProvidersDocsGenerator.java

@@ -40,7 +40,8 @@ public class ProvidersDocsGenerator {
     private final Set<Class<?>> subTypes = new TreeSet<>(providersComparatorBySimpleName);
 
     // Exclude non-providers from generation
-    private static final Set<String> providersToExcludeFromGeneration = Set.of("CustomFakerTest", "InsectFromFile", "Insect");
+    private static final Set<String> providersToExcludeFromGeneration =
+        Set.of("CustomFakerTest", "InsectFromFile", "Insect", "GizmoCustomTestFaker", "WidgetCustomTestFaker");
 
     private final Set<String> fakersWithoutSinceTag = new HashSet<>();
 
@@ -74,7 +75,7 @@ void generateProvidersDocs(BufferedWriter writer) throws IOException {
         System.out.println("Providers without '@since' tag: " + fakersWithoutSinceTag);
     }
 
-    private String extractGroupName(Class<?> clazz) {
+    private static String extractGroupName(Class<?> clazz) {
         // `packageName` should be such format: net.datafaker.providers.<groupName> (e.g. base, sport, movie)
         String packageName = clazz.getPackage().getName();
         // And just splitting by '.' we're getting groupName (e.g. base, sport, movie)
@@ -143,7 +144,7 @@ private String providersPerVersionTable() {
         Map<String, Integer> providersPerVersion = extractProvidersPerVersion();
 
         StringBuilder sb = new StringBuilder()
-            .append("\nNumber of providers per Datafaker version\n")
+            .append("\nNumber of providers per Datafaker version:\n")
             .append("\n| Version | Number of new providers | Total number of providers |")
             .append("\n|---------|-------------------------|---------------------------|\n");
 
@@ -180,7 +181,7 @@ private Map<String, Integer> extractProvidersPerVersion() {
         return providersPerVersion;
     }
 
-    private String formatGroupName(String groupName) {
+    private static String formatGroupName(String groupName) {
         return Character.toUpperCase(groupName.charAt(0)) + groupName.substring(1);
     }