diff --git a/.gitignore b/.gitignore
index be8aea3649..b2738b0bf0 100644
--- a/.gitignore
+++ b/.gitignore
@@ -44,7 +44,7 @@ print.prt
 */tsts/*/output/*
 */build/
 build/
-*/install/
+install/
 
 # Created by https://www.gitignore.io/api/macos
 # Edit at https://www.gitignore.io/?templates=macos
diff --git a/isis/src/base/objs/LineEquation/LineEquation.cpp b/isis/src/base/objs/LineEquation/LineEquation.cpp
index b7d08ddc6a..04efba3a22 100644
--- a/isis/src/base/objs/LineEquation/LineEquation.cpp
+++ b/isis/src/base/objs/LineEquation/LineEquation.cpp
@@ -90,6 +90,7 @@ namespace Isis {
     }
     else if(!p_slopeDefined) {
       p_slope = (p_y[0] - p_y[1]) / (p_x[0] - p_x[1]);
+      p_slopeDefined = true;
     }
     return p_slope;
   }
@@ -110,6 +111,7 @@ namespace Isis {
     }
     else if(!p_interceptDefined) {
       p_intercept = p_y[0] - Slope() * p_x[0];
+      p_interceptDefined = true;
     }
 
     return p_intercept;
diff --git a/isis/src/base/objs/LineEquation/LineEquation.truth b/isis/src/base/objs/LineEquation/LineEquation.truth
deleted file mode 100644
index 29e90dc1fe..0000000000
--- a/isis/src/base/objs/LineEquation/LineEquation.truth
+++ /dev/null
@@ -1,7 +0,0 @@
-Unit test for LineEquation
-Testing first constructor...
-     Slope = 2.5
-     Intercept = -1.5
-Testing second constructor...
-     Slope = -0.5
-     Intercept = 0.5
diff --git a/isis/src/base/objs/LineEquation/unitTest.cpp b/isis/src/base/objs/LineEquation/unitTest.cpp
deleted file mode 100644
index 90adb00b01..0000000000
--- a/isis/src/base/objs/LineEquation/unitTest.cpp
+++ /dev/null
@@ -1,30 +0,0 @@
-#include <iostream>
-#include <iomanip>
-#include "LineEquation.h"
-#include "FileName.h"
-#include "Preference.h"
-#include "Table.h"
-
-
-
-using namespace std;
-
-int main(int argc, char *argv[]) {
-  Isis::Preference::Preferences(true);
-
-  cout << setprecision(8);
-  cout << "Unit test for LineEquation" << endl;
-
-  cout << "Testing first constructor..." << endl;
-  Isis::LineEquation line1;
-  line1.AddPoint(1., 1.);
-  line1.AddPoint(3., 6.);
-  cout << "     Slope = " << line1.Slope() << endl;
-  cout << "     Intercept = " << line1.Intercept() << endl;
-
-  cout << "Testing second constructor..." << endl;
-  Isis::LineEquation line2(-1., 1., -3., 2.);
-  cout << "     Slope = " << line2.Slope() << endl;
-  cout << "     Intercept = " << line2.Intercept() << endl;
-
-}
diff --git a/isis/tests/LineEquationTests.cpp b/isis/tests/LineEquationTests.cpp
new file mode 100644
index 0000000000..549c0da07a
--- /dev/null
+++ b/isis/tests/LineEquationTests.cpp
@@ -0,0 +1,173 @@
+#include <gtest/gtest.h>
+#include "LineEquation.h"
+#include "IException.h"
+#include "TestUtilities.h"
+
+TEST(LineEquation, DefaultConstructor)
+{
+  Isis::LineEquation testEquation;
+
+  EXPECT_FALSE(testEquation.Defined());
+  EXPECT_FALSE(testEquation.HaveSlope());
+  EXPECT_FALSE(testEquation.HaveIntercept());
+  EXPECT_EQ(testEquation.Points(), 0);
+}
+
+TEST(LineEquation, InitConstructor)
+{
+  Isis::LineEquation testEquation(1.0, 2.0, 3.0, 4.0);
+
+  EXPECT_TRUE(testEquation.Defined());
+  EXPECT_TRUE(testEquation.HaveSlope());
+  EXPECT_TRUE(testEquation.HaveIntercept());
+
+  EXPECT_DOUBLE_EQ(testEquation.Slope(), 1.0);
+  EXPECT_DOUBLE_EQ(testEquation.Intercept(), 1.0);
+  EXPECT_EQ(testEquation.Points(), 2);
+}
+
+TEST(LineEquation, AddingPoints)
+{
+  Isis::LineEquation testEquation;
+
+  testEquation.AddPoint(1.0,2.0);
+
+  EXPECT_EQ(testEquation.Points(), 1);
+  EXPECT_FALSE(testEquation.HaveSlope());
+  EXPECT_FALSE(testEquation.HaveIntercept());
+  EXPECT_FALSE(testEquation.Defined());
+
+  testEquation.AddPoint(3.0,4.0);
+
+  EXPECT_EQ(testEquation.Points(), 2);
+  EXPECT_FALSE(testEquation.HaveSlope());
+  EXPECT_FALSE(testEquation.HaveIntercept());
+  EXPECT_TRUE(testEquation.Defined());
+  EXPECT_DOUBLE_EQ(testEquation.Slope(), 1.0);
+  EXPECT_DOUBLE_EQ(testEquation.Intercept(), 1.0);
+  EXPECT_TRUE(testEquation.HaveSlope());
+  EXPECT_TRUE(testEquation.HaveIntercept());
+
+  try
+  {
+    testEquation.AddPoint(5.0, 6.0);
+    FAIL() << "Expected an exception to be thrown";
+  }
+  catch(Isis::IException &e)
+  {
+    EXPECT_TRUE(e.toString().toLatin1().contains("Line equation is already defined"))
+      << e.toString().toStdString();
+  }
+  catch(...)
+  {
+    FAIL() << "Expected an IException with message:"
+      "\"Line equation is already defined with 2 points\"";
+  }
+
+  EXPECT_EQ(testEquation.Points(), 2);
+  EXPECT_TRUE(testEquation.HaveSlope());
+  EXPECT_TRUE(testEquation.HaveIntercept());
+  EXPECT_TRUE(testEquation.Defined());
+  EXPECT_DOUBLE_EQ(testEquation.Slope(), 1.0);
+  EXPECT_DOUBLE_EQ(testEquation.Intercept(), 1.0);
+}
+
+TEST(LineEquation, UndefinedSlope)
+{
+  Isis::LineEquation testEquation;
+
+  try
+  {
+    testEquation.Slope();
+    FAIL() << "Expected an exception to be thrown";
+  }
+  catch(Isis::IException &e)
+  {
+    EXPECT_TRUE(e.toString().toLatin1().contains("Line equation undefined"))
+      <<e.toString().toStdString();
+  }
+  catch(...)
+  {
+    FAIL() << "Expected an IException with message:"
+      "\"Line equation undefined:  2 points are required\"";
+  }
+}
+
+TEST(LineEquation, UndefinedIntercept)
+{
+  Isis::LineEquation testEquation;
+
+  try
+  {
+    testEquation.Intercept();
+    FAIL() << "Expected an exception to be thrown";
+  }
+  catch(Isis::IException &e)
+  {
+    EXPECT_TRUE(e.toString().toLatin1().contains("Line equation undefined"))
+      <<e.toString().toStdString();
+  }
+  catch(...)
+  {
+    FAIL() << "Expected an IException with message:"
+     " \"Line equation undefined:  2 points are required\"";
+  }
+}
+
+TEST(LineEquation, AddSamePoints)
+{
+  Isis::LineEquation testEquation;
+  testEquation.AddPoint(1.0,1.0);
+  testEquation.AddPoint(1.0,1.0);
+
+  try
+  {
+    testEquation.Intercept();
+    FAIL() << "Expected an exception to be thrown";
+  }
+  catch(Isis::IException &e)
+  {
+    EXPECT_TRUE(e.toString().toLatin1().contains("Points have identical"))
+      <<e.toString().toStdString();
+  }
+  catch(...)
+  {
+    FAIL() << "Expected an IException with message:"
+      "\"Points have identical independent variables -- no intercept\"";
+  }
+
+  try
+  {
+    testEquation.Slope();
+    FAIL() << "Expected an exception to be thrown";
+  }
+  catch(Isis::IException &e)
+  {
+    EXPECT_TRUE(e.toString().toLatin1().contains("Points have identical"))
+      <<e.toString().toStdString();
+  }
+  catch(...)
+  {
+    FAIL() << "Expected an IException with message:"
+      "\"Points have identical independent variables -- no slope\"";
+  }
+}
+
+TEST(LineEquation, InitSamePoints)
+{
+  try
+  {
+    Isis::LineEquation testEquation(1.0,1.0,1.0,1.0);
+    FAIL() << "Expected an exception to be thrown";
+  }
+  catch(Isis::IException &e)
+  {
+    EXPECT_TRUE(e.toString().toLatin1().contains("Points have identical"))
+      <<e.toString().toStdString();
+  }
+  catch(...)
+  {
+    FAIL() << "Expected an IException with message:"
+      "\"Points have identical independent variables -- no intercept\"";
+  }
+}