MA0185: Add tests and docs for literal-only interpolated strings

docs/Rules/MA0185.md

@@ -3,9 +3,15 @@
 Sources: [SimplifyStringCreateWhenAllParametersAreCultureInvariantAnalyzer.cs](https://github.com/meziantou/Meziantou.Analyzer/blob/main/src/Meziantou.Analyzer/Rules/SimplifyStringCreateWhenAllParametersAreCultureInvariantAnalyzer.cs), [SimplifyStringCreateWhenAllParametersAreCultureInvariantFixer.cs](https://github.com/meziantou/Meziantou.Analyzer/blob/main/src/Meziantou.Analyzer.CodeFixers/Rules/SimplifyStringCreateWhenAllParametersAreCultureInvariantFixer.cs)
 <!-- sources -->
 
-When using `string.Create(CultureInfo.InvariantCulture, ...)` with an interpolated string where all parameters are culture-invariant, you can simplify the code by using a simple interpolated string instead.
+When using `string.Create(CultureInfo.InvariantCulture, ...)` with an interpolated string where all parameters are culture-invariant (or no parameters at all), you can simplify the code by using a simple interpolated string instead.
 
 ````c#
+// ❌ Unnecessary use of string.Create with literal-only string
+var a = string.Create(CultureInfo.InvariantCulture, $"string without parameters.");
+
+// ✅ Simplified version
+var b = $"string without parameters.";
+
 // ❌ Unnecessary use of string.Create with culture-invariant parameters
 var x = string.Create(CultureInfo.InvariantCulture, $"Current time is {DateTime.Now:O}.");
 
@@ -14,6 +20,7 @@ var y = $"Current time is {DateTime.Now:O}.";
 ````
 
 The analyzer detects when all interpolated values are culture-invariant, such as:
+- **No parameters at all** (literal-only interpolated strings)
 - Strings
 - GUIDs
 - DateTime with invariant formats (O, o, R, r, s, u)

tests/Meziantou.Analyzer.Test/Rules/SimplifyStringCreateWhenAllParametersAreCultureInvariantAnalyzerTests.cs

@@ -290,5 +290,77 @@ await CreateProjectBuilder()
               .WithSourceCode(SourceCode)
               .ValidateAsync();
     }
+
+    [Fact]
+    public async Task StringCreateWithInvariantCulture_EmptyString_ShouldReport()
+    {
+        const string SourceCode = """
+using System;
+using System.Globalization;
+
+class TypeName
+{
+    public void Test()
+    {
+        var x = [|string.Create(CultureInfo.InvariantCulture, $"")|];
+    }
+}
+""";
+
+        const string Fix = """
+using System;
+using System.Globalization;
+
+class TypeName
+{
+    public void Test()
+    {
+        var x = $"";
+    }
+}
+""";
+        await CreateProjectBuilder()
+              .WithLanguageVersion(Microsoft.CodeAnalysis.CSharp.LanguageVersion.CSharp10)
+              .WithTargetFramework(TargetFramework.Net6_0)
+              .WithSourceCode(SourceCode)
+              .ShouldFixCodeWith(Fix)
+              .ValidateAsync();
+    }
+
+    [Fact]
+    public async Task StringCreateWithInvariantCulture_MultipleWords_ShouldReport()
+    {
+        const string SourceCode = """
+using System;
+using System.Globalization;
+
+class TypeName
+{
+    public void Test()
+    {
+        var x = [|string.Create(CultureInfo.InvariantCulture, $"This is a test message without any interpolations")|];
+    }
+}
+""";
+
+        const string Fix = """
+using System;
+using System.Globalization;
+
+class TypeName
+{
+    public void Test()
+    {
+        var x = $"This is a test message without any interpolations";
+    }
+}
+""";
+        await CreateProjectBuilder()
+              .WithLanguageVersion(Microsoft.CodeAnalysis.CSharp.LanguageVersion.CSharp10)
+              .WithTargetFramework(TargetFramework.Net6_0)
+              .WithSourceCode(SourceCode)
+              .ShouldFixCodeWith(Fix)
+              .ValidateAsync();
+    }
 #endif
 }