System.Tests.StringTests.IndexOf_AllSubstrings C# (CSharp) Method

        public static void IndexOf_AllSubstrings(string s, string value, int startIndex, StringComparison comparison)
        {
            bool ignoringCase = comparison == StringComparison.OrdinalIgnoreCase || comparison == StringComparison.CurrentCultureIgnoreCase;

            // First find the substring.  We should be able to with all comparison types.
            Assert.Equal(startIndex, s.IndexOf(value, comparison)); // in the whole string
            Assert.Equal(startIndex, s.IndexOf(value, startIndex, comparison)); // starting at substring
            if (startIndex > 0)
            {
                Assert.Equal(startIndex, s.IndexOf(value, startIndex - 1, comparison)); // starting just before substring
            }
            Assert.Equal(-1, s.IndexOf(value, startIndex + 1, comparison)); // starting just after start of substring

            // Shouldn't be able to find the substring if the count is less than substring's length
            Assert.Equal(-1, s.IndexOf(value, 0, value.Length - 1, comparison));

            // Now double the source.  Make sure we find the first copy of the substring.
            int halfLen = s.Length;
            s += s;
            Assert.Equal(startIndex, s.IndexOf(value, comparison));

            // Now change the case of a letter.
            s = s.ToUpperInvariant();
            Assert.Equal(ignoringCase ? startIndex : -1, s.IndexOf(value, comparison));
        }