Add unit tests

Author: sji-buttercup

oauth2/core/src/test/java/com/dremio/iceberg/authmgr/oauth2/config/ClientAssertionConfigTest.java

@@ -149,4 +149,44 @@ void testKeyIdPresent() {
         smallRyeConfig.getConfigMapping(ClientAssertionConfig.class, PREFIX);
     assertThat(config.getKeyId()).hasValue("my-key-123");
   }
+
+  @Test
+  void testAudienceSingle() {
+    Map<String, String> properties =
+        Map.of(PREFIX + '.' + ClientAssertionConfig.AUDIENCE, "https://auth.example.com");
+    SmallRyeConfig smallRyeConfig =
+        new SmallRyeConfigBuilder()
+            .withMapping(ClientAssertionConfig.class, PREFIX)
+            .withSources(new MapBackedConfigSource("catalog-properties", properties, 1000) {})
+            .build();
+    ClientAssertionConfig config =
+        smallRyeConfig.getConfigMapping(ClientAssertionConfig.class, PREFIX);
+    assertThat(config.getAudience())
+        .hasSize(1)
+        .extracting("value")
+        .containsExactly("https://auth.example.com");
+    assertThat(config.getAudienceString()).hasValue("https://auth.example.com");
+  }
+
+  @Test
+  void testAudienceMultiple() {
+    Map<String, String> properties =
+        Map.of(
+            PREFIX + '.' + ClientAssertionConfig.AUDIENCE,
+            "https://auth1.example.com,https://auth2.example.com,https://auth3.example.com");
+    SmallRyeConfig smallRyeConfig =
+        new SmallRyeConfigBuilder()
+            .withMapping(ClientAssertionConfig.class, PREFIX)
+            .withSources(new MapBackedConfigSource("catalog-properties", properties, 1000) {})
+            .build();
+    ClientAssertionConfig config =
+        smallRyeConfig.getConfigMapping(ClientAssertionConfig.class, PREFIX);
+    assertThat(config.getAudience())
+        .hasSize(3)
+        .extracting("value")
+        .containsExactly(
+            "https://auth1.example.com", "https://auth2.example.com", "https://auth3.example.com");
+    assertThat(config.getAudienceString())
+        .hasValue("https://auth1.example.com,https://auth2.example.com,https://auth3.example.com");
+  }
 }