Add failing test for missing source-branch config

src/GitVersionCore.Tests/Configuration/ConfigProviderTests.cs

@@ -117,6 +117,38 @@ public void SourceBranchIsRequired()
                                 "See https://gitversion.net/docs/configuration/ for more info");
         }
 
+        [Test(Description = "This test proves the configuration validation will fail early with a helpful message when a branch listed in source-branches has no configuration.")]
+        public void SourceBranchesValidationShouldFailWhenMatchingBranchConfigurationIsMissing()
+        {
+            const string text = @"
+branches:
+    bug:
+        regex: 'bug[/-]'
+        tag: bugfix
+        source-branches: [notconfigured]";
+            SetupConfigFileContent(text);
+            var ex = Should.Throw<ConfigurationException>(() => configProvider.Provide(repoPath));
+            ex.Message.ShouldBe($"Branch configuration 'bug' defines these 'source-branches' that are not configured: '[notconfigured]'{Environment.NewLine}" +
+                                "See https://gitversion.net/docs/configuration/ for more info");
+        }
+
+        [Test(Description = "Well-known branches may not be present in the configuration file. This test confirms the validation check succeeds when the source-branches configuration contain these well-known branches.")]
+        [TestCase(Config.MasterBranchKey)]
+        [TestCase(Config.DevelopBranchKey)]
+        public void SourceBranchesValidationShouldSucceedForWellKnownBranches(string wellKnownBranchKey)
+        {
+            var text = $@"
+branches:
+    bug:
+        regex: 'bug[/-]'
+        tag: bugfix
+        source-branches: [{wellKnownBranchKey}]";
+            SetupConfigFileContent(text);
+            var config = configProvider.Provide(repoPath);
+
+            config.Branches["bug"].SourceBranches.ShouldBe(new List<string> { wellKnownBranchKey });
+        }
+
         [Test]
         public void CanProvideConfigForNewBranch()
         {

src/GitVersionCore/Configuration/ConfigurationBuilder.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Collections.Generic;
+using System.Linq;
 using GitVersion.Extensions;
 using GitVersion.Model.Configuration;
 using GitVersion.VersionCalculation;
@@ -162,6 +163,10 @@ private static void ValidateConfiguration(Config config)
                 {
                     throw new ConfigurationException($"Branch configuration '{name}' is missing required configuration 'source-branches'{System.Environment.NewLine}" + "See https://gitversion.net/docs/configuration/ for more info");
                 }
+
+                var missingSourceBranches = sourceBranches.Where(sb => !config.Branches.ContainsKey(sb)).ToArray();
+                if (missingSourceBranches.Any())
+                    throw new ConfigurationException($"Branch configuration '{name}' defines these 'source-branches' that are not configured: '[{string.Join(",", missingSourceBranches)}]'{System.Environment.NewLine}" + "See https://gitversion.net/docs/configuration/ for more info");
             }
         }